Questions. I Have Them.

Why is it that when some old motherfucker tries to explain how begrudgingly they're okay with gay people or any other "nontraditional" sexual relationship they dismiss their intimate relations by always using the phrase, "get up to", as in "hey, I don't care what they get up to in the privacy of their own bedroom"? The hit rate for this is like 100%, and I've literally never heard any of them refer to heterosexual activity in such a way, so...dafuck? 🤔🤷‍♂️