This link deals with that.
It’s a Jewish take on Genesis 6.
The idea of fallen angels (which is quite Biblical) in Genesis 6 is just hard to present to "modern man."
But the point is, it doesn't matter whether "modern man" can accept it or not, the Bible quite clearly states that Genesis 6 is about fallen angels.
Heiser, who also taught in seminaries, said that political correctness in its broadest definition isn't a new phenomenon. This is the reason seminaries avoid the discussion of angels in general. Same for rabbis. The spiritual realm just isn't "politically correct" because it sounds primitive.
Ignoring the spiritual realm in general is like glossing over the parting of the Red Sea or Jonah and the whale...or other miraculous events. Modernists just don't want to hear about miracles. They only want "science" and the subject of angels doesn't sound scientific.