[Pseudoscience-is-malarkey (OP)]

I think it's just another cult like fantasy. There is no other mention of it's existence outside Plato's blurb. It's supposedly was a technological and socially advanced western civilization that proceeded Greece.

[Petrochemicals]

That is because a great calamity befell the island wiping the history from the map. Much like the city of pompeii with its famed dick pics.