Question: Why do we not have much information about the matter that forms the black holes?
About the article "Black hole", section "Information loss paradox".

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Because a black hole has only a few internal parameters, most of the information about the matter that went into forming the black hole is lost.
Regardless of the type of matter which goes into a black hole, it appears that only information concerning the total mass, charge, and angular momentum are conserved.
As long as black holes were thought to persist forever this information loss is not that problematic, as the information can be thought of as existing inside the black hole, inaccessible from the outside.
However, black holes slowly evaporate by emitting Hawking radiation.
This radiation does not appear to carry any additional information about the matter that formed the black hole, meaning that this information appears to be gone forever.
The question whether information is truly lost in black holes (the black hole information paradox) has divided the theoretical physics community (see Thorne–Hawking–Preskill bet).
In quantum mechanics, loss of information corresponds to the violation of vital property called unitarity, which has to do with the conservation of probability.
It has been argued that loss of unitarity would also imply violation of conservation of energy.
Over recent years evidence has been building that indeed information and unitarity are preserved in a full quantum gravitational treatment of the problem.
Objection: " great many things have been explained by matter and motion…."
Natural science has made much progress by assuming the existence of matter and mechanical motion.
Answer: Scientists do not need to assume that matter and motion exist and that they have effects on an observer's mind.
All scientists need to do is to explain why we are affected by certain "ideas" on certain occasions. 
Stephen Hawking often speaks of the thermodynamic entropy of black holes in terms of their information content.
Do black holes destroy information?
It appears that there are deep relations between the entropy of a black hole and information loss See "Black hole thermodynamics" and "Black hole information paradox". 
The evidence for stellar black holes strongly relies on the existence of an upper limit for the mass of a neutron star.
The size of this limit heavily depends on the assumptions made about the properties of dense matter.
New exotic phases of matter could push up this bound.
A phase of free quarks at high density might allow the existence of dense quark stars, and some supersymmetric models predict the existence of Q stars.
Some extensions of the standard model posit the existence of preons as fundamental building blocks of quarks and leptons, which could hypothetically form preon stars.
These hypothetical models could potentially explain a number of observations of stellar black hole candidates.
However, it can be shown from general arguments in general relativity that any such object will have a maximum mass.
Since the average density of a black hole inside its Schwarzschild radius is inversely proportional to the square of its mass, supermassive black holes are much less dense than stellar black holes (the average density of a 108 solar mass black hole is comparable to that of water).
Consequently, the physics of matter forming a supermassive black hole is much better understood and the possible alternative explanations for supermassive black hole observations are much more mundane.
For example, a supermassive black hole could be modelled by a large cluster of very dark objects.
However, such alternatives are typically not stable enough to explain the supermassive black hole candidates.
The evidence for stellar and supermassive black holes implies that in order for black holes not to form, general relativity must fail as a theory of gravity, perhaps due to the onset of quantum mechanical corrections.
A much anticipated feature of a theory of quantum gravity is that it will not feature singularities or event horizons (and thus no black holes).
In 2002, much attention has been drawn by the fuzzball model in string theory.
Based on calculations in specific situations in string theory, the proposal suggests that generically the individual states of a black hole solution do not have an event horizon or singularity, but that for a classical/semi-classical observer the statistical average of such states does appear just like an ordinary black hole in general relativity. 
One way to detect primordial black holes is by their Hawking radiation.
Stephen Hawking theorized in 1974 that large numbers of such smaller primordial black holes might exist in the Milky Way in our galaxy's Halo region.
All black holes are theorized to emit Hawking radiation at a rate inversely proportional to their mass.
Since this emission further decreases their mass, black holes with very small mass would experience runaway evaporation, creating a massive burst of radiation at the final phase, equivalent to a hydrogen bomb yielding millions of megatons of explosive force.
A regular black hole (of about 3 solar masses) cannot lose all of its mass within the current age of the universe (they would take about 1069 years to do so, even without any matter falling in).
However, since primordial black holes are not formed by stellar core collapse, they may be of any size.
A black hole with a mass of about 1011 kg would have a lifetime about equal to the age of the universe.
If such low-mass black holes were created in sufficient number in the Big Bang, we should be able to observe some of those that are relatively nearby in our own Milky Way galaxy exploding today.
NASA's Fermi Gamma-ray Space Telescope satellite, launched in June 2008, is designed in part to search for such evaporating primordial black holes.
However, if theoretical Hawking radiation does not actually exist, such primordial black holes would be extremely difficult, if not impossible, to detect in space due to their small size and lack of large gravitational influence.
It has been suggested that a small black hole passing through the Earth would produce a detectable acoustic signal.
Because of its tiny diameter, large mass compared to a nucleon, and relatively high speed, such primordial black holes would simply transit Earth virtually unimpeded with only a few impacts on nucleons, exiting the planet with no ill effects.
Another way to detect primordial black holes could be by watching for ripples on the surfaces of stars.
If the black hole passed through a star, its density would cause observable vibrations.