Evolution doesn't necessarily revisit decisions.

On the frontier a lot of random stuff is tried.

Most fade away, consumed by entropy.

But some subset turn out to be useful and continue to be invested in because of that usefulness.

They become a stable platform for other things to accumulate on top of.

The top layer is fragile, but once things are built on top it becomes durable and load bearing, even if it's a bit suboptimal or weird.