Apple is very aggressive about requiring the latest OS.
For example, XCode requires 15.2 or later.. which came out in December.
15.2 supports machines as far back as 2017, so I'm not really seeing that as a big issue. But again, the larger point is that a machine that's not supported by MacOS 26 works just as well at this moment (and for quite a while in the future) as it did before the keynote. It's not suddenly more vulnerable; the software on it hasn't magically stopped working. It's just a workable as it was a few hours ago.