That seems like a policy decision that can and should be made by the company, not Microsoft: Microsoft should feel free to release patches on any day they want, and if a common accepted practice is for IT departments to have a staged rollout of cleared patches, that sounds awesome. If I want "patch Tuesday" or even "patch Wednesday", it seems trivial for me to just do that myself.
It was made at the request of the companies so there could be a coordinated day. Once the patches are out they can be exploited, so having a coordinated day helps to ensure everyone can get patched in time.
Again, Microsoft only changed because their customers asked, basically demanded, that they do it that way. It wasn't really MS's decision, it was them responding to their biggest customers.
Microsoft doesn’t want to — they want to bundle as much as possible into patch releases these days, and push as many things into new builds as possible.
