as opposed to... putting all of our eggs in any number of CA baskets, where the CA's are basically random companies of random ethics in random locations and where the loss of any one of our eggs means the loss of ALL of them?

It's already gone bad for the security field ;)

With ongoing certificate transparency efforts I'm less worried about this..

Nothing stops any of the big CA's to offer their own ACME endpoint. It's an open standpoint based on software that is on github.

Running a ACME authority is not hard. The CA's just don't want to cannibalize their business.

At least one major commercial CA does offer ACME to paying customers. If you want ACME and want to use their CA, and have whatever their entry level enterprise price is burning a hole in your pocket, they will take your money.

They basically position it as "As well as integrating with Windows we also make everything work automatically with your weird Unix stuff like Apache or nginx" but it's an ACME service under the hood.

ACMEv2 (the Internet Standard RFC when that finally gets published) is a bit nicer for a commercial CA because it spells out how you use ACME to say e.g. "Hey, I'm paying customer #383829, here is proof - give me certificates on my account". The only easy way this could have worked in ACMEv1 wasn't terribly compatible with the limited understanding of cryptography that say Steve in accounting has.