What factor prevents us from finding fossils from the precambrian era?

Am certain that the factor that prevents us from finding fossils from the Precambian era is that Most rocks from that era are deeply buried.  The precambrian is the informal name for the large expanse of time preceding the current Phanerozoic Eon. It began with the Earh's Formation about 4.5 billion years ago and lasted until the advent of multicellular life about 542 million years ago.