I think it's probably because we've shifted away from shipping software as a product, and onto software as a service. I.E. in the 90s if win 95 irreversibly corrupted, that would be devastating to sales.

But today with windows 11? Just roll it out in one of the twenty three testing branches you have and see what happens, and if shit does break. Just work around it. It'll be fine. Even if something does happen, you can most of the time, fix it and roll out a new update.

And i also think it's moved to be more team centric, rather than department centric. A lot of the theory is probably more senior team led type responsibility. While everyone writing the code can chip in and add some as well. Developers knowing how to write secure code helps, so they should theoretically also be capable of QA themselves to a degree.

Also there's a lot more money in shipping shit out the door, than there is in shipping a functional product, unfortunately.