The problem with QA is that from the POV of management, all they do is find issues and delay releases. If the QA team did their jobs well, then once all of the reported bugs are found and fixed (passes QA), the software runs fine and there are no future problems. This sounds good in theory, but a good release doesn't get the credit it deserves - it's "business as usual".

A buggy release is fine, if it came out faster, and costed less. The bugs in the release can be fixed in the future, and the "heroic" fixes are "creditworthy".

Therefore, over time, the QA team is politically relegated as a "useless" team in the department, and thus given how politics play out, they get sidelined until the entire team is gone.