Microfossils like some kinds of plankton are common, although you need a microscope to see them. So lets confine ourselves to large macroscopic fossils. 1. read more
There aren't a lot of people looking for fossils. The world is a pretty big place. Even when fossils are found it takes time to identify them. Some of the larger finds made in the last couple decades have come from museum collections that have yet to be studied. read more
We don't know if there aren't fossils on Mars. We've barely looked anywhere there. So there might be. Fossils require a lot of circumstances to be just right to come about. Not the least of which is water. Also, hard body parts (shells, bones, etc.) help a lot. read more
In addition, many dinosaur bearing sediments eroded away long ago or were buried deeply under more recent sediments, so the bones can't be found. Edit: dinosaurs DID live essentially everywhere on the planet. Their remains have been found even in high latitude (polar dinosaur) habitats, and in the arid habitats of the Gobi. read more