There is a great deal of theoretical work which suggests that WIMPs exist and probably account for a large fraction of dark matter. If you don't believe that WIMPs exist, you aren't alone. Big bang nucleosynthesis limits the total number of baryons to be a fraction of the Universes total mass. Note the use of the word exotic. Neutrinos are another type of non-baryonic particle, but are not considered exotic.
Neutrinos do exist, in huge numbers, but all known neutrinos have zero mass.
The search continues for neutrinos with mass, but a massive neutrino is unlikely to completely account for the flat nature of galactic rotation curves. Hence, an exotic class of non-baryonic dark matter particle must exist if WIMPs do not. There are several candidates for baryonic dark matter. Although we can see Jupiter quite well from Earth, chances are that someone looking at our solar system from any far distance would not be able to see Jupiter. So, it is reasonable to assume that there are Jupiter-sized objects in other solar systems that we cannot see.