Microsoft used to have a really good reputation for developers. Used to one of the few companies where each developer had their own office.
My personal experience, having worked on a few skunkworks projects over there with a couple of different teams was that there were two people to an office that was probably originally designed for one. It was a bit cozy in there for my liking but it wasn't cramped, it was quiet, and a couple of people could stand in various parts of common areas and have an actual 'stand up' collaboration. It actually seemed very collegiate. I recognize the fact that since it was an R&D group they probably had better accommodations for this type of stuff, and that they were in an 'old' building that had these personal offices probably helped too.
A large part is probably demographics of developers is now changing.
Demographics are a factor. Lots of devs, especially younger devs, and especially devs who've worked at other younger companies are asking for open floor plans. Not all of them, but a sizable chunk. That plus reduced cost for providing office space to devs is pushing the company in the direction of open office spaces. I haven't seen a building get significantly renovated and not end up with open spaces.
None of my friends (all in their 20s) prefer open offices.
I'm also not sure how old you think I am. I'm 34, not 74.
I'm 23, have heard of Extreme Programming, and absolutely want my own private office (and, failing that, a silent shared work space).
Although I should say our whole team works 1-2 days from home. Different people, different days and we're very okay with that.
We also like to leave developers who have headphones alone and only talk to them over skype/slack.
As a consultant, that office does happen to be in my home. But I wouldn't return to a FT gig without having a place where I can go, separating from "home", to work in productive quiet.
It doesn't make sense to gut the interior just to make a slightly different private office configuration, so it probably isn't considered a "significant" renovation.
Neruodiversity is a real thing that we should be thinking about.
To support your point: a number of people have voluntarily taken over a former conference room to turn it into an open space office.
Personally I have worked in both and don't find one better or worse than the other. I actually value sunlight, direct or indirect, more than the layout.
Note that the post you're replying to uses the past tense. The vast majority of my tenure at MSFT was in a private office, but that was over ten years ago. It is my understanding that things have changed since.