Why didn't more pros use Kevlar strings before poly?

I mean, of course, before poly was being sold.

Yes of course Agassi did. But nobody else?

Wasn't there a real advantage to be had from playing with them? Why did none of them take it?

I don't buy the arm-harshness reason. Pros use all sorts of setups that would be hard on the arm of an amateur.

It seems like a missed opportunity...