I also think its fine and fair to charge for the general GHA infrastructure that one would also be using with self-hosted runners.

I suspect that they weren't looking to make money off of those charges, but rather use that as a forcing function to push more usage of their managed runner (which are higher margin) which didn't work out. Rather than everyone saying "damn that makes alternatives financially unattactive", a good chunk of the feedback was "sure I'll pay those charges as long as I don't have to use the shitty managed runners".