I don't know why you'd believe they've ever been capable of putting out quality software.

A bug in the software is a bug in the process, and the process is the job of leadership. They've never cared about software quality. They'll put out lots of books about it, lots of talks, lots of claims. But they won't actually put out quality software. It's not in their DNA, never was.

It's not their size nor their age that makes this hard for them. Plenty of larger, older companies put out better product ever day. It's just them. Someone in each size class is the best, and someone else is the worst. MS has been the worst the entire time.