Like all other job functions tangential to development- it can be difficult to organize the labor needed to accomplish this within a single team, and it can be difficult to align incentives when the labor is spread across multiple teams.

This gets more and more difficult with modern development practices. Development benefits greatly from fast release cycles and quick iteration- the other job functions do not! QA is certainly included there.

I think that inherent conflict is what is causing developers to increasingly managing their own operations, technical writing, testing, etc.