I'd flip this around and say that serious philosophers
do have sufficient grounding in mathematics and physics, by definition: without it, you can't have serious philosophy.
Now by "sufficient grounding" I don't mean formal education and title. The point I'm making is that STEM fields provide grounding that's necessary but not sufficient to do proper philosophy, and humanities provide information that, while valuable and useful, is neither necessary nor sufficient.
If you accept that premise, then it's obvious from pure statistics that you'll find better philosophy in STEM circles than humanities, simply because it's more likely a philosophically inclined mind there had a chance to acquire the necessary grounding (whether due to formal schooling or personal interests).