Well they did hire them, why wouldn't they be tied to them?
Because in the spirit of the Catholic tradition, the value of academic excellence supersedes any tether to religious purity. The Universities purposefully hire professors who may not be Catholics, Christians or people of any faith. Why? Because they owe it to their students to provide to them the brightest minds and subject-matter experts in their fields of study.
It should not be a surprise to anyone when some of those professors disagree with Church doctrine. And, it should be no surprise that those professors may be active off-campus in some of those political, ideological, theological or philosophical pursuits.
If you want Catholic universities to only have Catholic professors and dogmatic adherents, then you don't want a university in the Catholic tradition. You want something else.