Hard to believe people are asking this question in 2026. Quality is something that takes dedicated focus and lots of work. Therefore it’s a job, not an afterthought or latest priority for someone whose primary focus is not quality.
So why would you outsource it to another team that isn't doing the actual work?
But on other hand those people can not often be trusted. As such you need a team that does checks again. Or alternatively they might have misunderstood something and thus produced incorrect system. Or there is some other fault in their thought process or reality. And system operates differently in more real scenario.