@Khandro
I omitted to point out that, just as we see happening around the Pacific rim, in the present day, the ocean floor ***and all the fossils recorded in it*** are destroyed by the subduction zones.
The Atlantic started as a split down the middle of a supercontinent. Since it is 2500+ miles wide now, that's probably how much Pacific sea floor has been subducted and melted down.
The Appalachians and (some of) the mountains of Scotland and Ireland are supposed to have been when a previous ocean was lost, by subduction, between landmasses which joined to form the pre-Atlantic supercontinent. By analagous processes, oceans have 'opened and closed' over the aeons, so the fossil record of life in the deep oceans has been irretrievably erased.
The precambrian fossils in question are mostly sea creatures, from shallow seas and we only find them on land by virtue of their former sea bed now being a 'crumple zone', raised above sea level.
My 'pet' theory is that life evolved at extreme depth where high temperature (hydrothermal vents) and pressure helped drive biological-type chemical reactions and enzymes gradually allowed cooler, less deep waters to be exploited. The need for eyes did not arise until the shallows were reached by many iterations of refinement of enzyme function.
Phototaxis - swimming towards the light is precisely what photosynthetic multicellular life needed to do. Divergence into dedicated plant-like life and plant-eating life seems to have occured after phototaxis came about. Otherwise, it would have to evolve a second time by chance. This is not unknown (eg flight) but the odds of arriving at the same photosensitive proteins (opsins) and their respective DNA sequences would be highly improbable.
The preservation of genes from unicellular life upwards to higher organisms (with minor modifications) somewhat compensates us for the gaps in the fossil record.