Language is a powerful human talent. It's reasonable to assume that there have been many variants of writing systems throughout human evolution.
However, such systems would need to be widely adopted and durably preserved to survive millennia and eventually be rediscovered.
Which is how we happen to know the precious little that we do know about past writing systems.
> It's reasonable to assume that there have been many variants of writing systems throughout human evolution.
I don't find it that reasonable an assumption. As far as I know, there is no hunter-gatherer society that has developed writing, except societies who have had contact with a sedentary agricultural civilisation with writing.
Given that all human societies for which there's evidence were hunter-gatherers until about 10k years ago, to me it seems more reasonable to conclude they had no writing.
Now, you might say that agriculture and civilisation were around earlier, but we dhaven't found the evidence. But we do have evidence of plenty of human groups at those earlier times, and they're all hunter-gatherers.