This has been coming for a couple years already. I agree there are some organizations that probably didn't take GA4 seriously until this week, but I don't know how many of them were really delving into their historical analytics to begin with.
Anyway, I don't mean to take away from your moment to hate on Google. :) It's just not a classic Google discontinuation like when they eventually shut down Stadia or whatever.
The first announcement of the date. We all knew it was coming; I figured it would be many years in the future. I still think so, actually... I think Google is bluffing, because nobody is taking up GA4. Some are implementing it, in tandem with UA, but very few are using it.
Nobody wants to move to GA4. It has nothing UA doesn't, and UA has lots of features GA4 doesn't. If they're sunsetting UA next year, there's no way it'll have improved enough by then to be a fully functioning replacement. It has a cleaner structure than UA, because it's dropping a decade of cruft, but that doesn't really help when it just doesn't do as much.
The people that are moving to GA4 are running both UA and GA4 in parallel, so that they'll have a history set when UA shuts off. Those are companies that are paying attention. I would be surprised, by the 2023 date, if even 25% of the UA installations have switched to GA4. (Of course, all the larger companies will have.)
Side note... I looked into Shopify a month or two back. They have a drop in UA implementation that is almost as easy as clicking on a checkbox. Not only do they not have a wizard for implementing GA4, they say it's not even possible for you to add manually. No due date was given. A lot of sites have UA built in as the assumed forever default.
Anyway, I don't mean to take away from your moment to hate on Google. :) It's just not a classic Google discontinuation like when they eventually shut down Stadia or whatever.