As I understand it they discovered a long chain molecule which was highly inert and wouldn’t stick to anything. Which was a useful feature but you know makes it hard to attach to anything. So they created a similar smaller chain molecule which had a reactive tip but was still super stable. Unfortunately it’s also a bit amino acid like. So we ended up with a molecule which is very durable and accumulates in living things.

Then of course we produced it at industrial scale for decades flooding the entire planet with this stuff.