I have the same speculations re: why, so far, they have been so reluctant to do so.

As for why now? I believe it's simply because now that peons have had a taste of WFH and all its benefits (and realized everything you enumerated), it will become one of the most desired "benefit" in a job. It was a massive leap forward from WFH being a "nice to have" to a "must have" to even be considered by a lot of candidates.