Terrestrial organisms are less likely to be fossilized. Drier conditions tend not to transport the minerals needed for fossilization. Both environments have decay, scavengers, and erosion that can destroy remaining hard-parts that would other wise be candidates for fossilization. Trees are targeted by bacteria, fungi, molds, ants, and termites. Besides the biological agents which affect a corps, there are mechanical agents as well.
Rapid burial is the key in either habitat for fossilization.
Large items verses small items is another bias which exists. When it comes to discovering a fossil or for the tissue to withstand the environment to be fossilized in the first place, large items tend to last compared to that of small items. Another bias is sheer numbers verses rare organisms. Another big bias against fossils being discovered is their location. The problem is, most paleontologists are poking around in dry, warm environments and while these places may at one time have been sea front property, many locations that were aqueous are still aqueous.