I have been reading up about fossil algaes since quite a while, and cyanobacterias, as you can expect, very commonly come up when looking at papers concerning Palaeozoic reefs. However, there's been a certain element that seems quite... strange, concerning how fossil evidence is sorted. There seems to be a plethora of fossil generas and families erected for said fossils, stretching across seemingly absurd amounts of time, & upon closer inspection there seems to be several papers relating the observation of similar or almost identical forms among living genera, as well as fossils being recovered from very recent fossil deposits which would imply they just disappeared in an almost unnatural fashion just recently.

Since these generas and species are very often differentiated based on very small morphological differences (this mostly applies to species) and seem to have almost perfect replicas amongst living genera, then i ponder : what is the purpose of such families and generas if they essentially encompass just fossil equivalents of modern forms with very little differences between them ?

Wouldn't it be wiser to assign them to corresponding modern generas or families instead ? Or do they truly represent different organisms ?

I apologize if the question seems very intrusive but i cannot seem to found a conclusive answer anywhere else