I can't explain why "husband of one wife" is there. Certainly it is no sin to be the husband of more than one wife.
My inclination is to believe it has less to do with him being too busy, and more to do with the attitude an Elder is supposed to have.
Which is to say:
Woe, shepherds of Israel who have been feeding themselves! Should not the shepherds feed the flock? 3“You eat the fat and clothe yourselves with the wool, you slaughter the fat sheep without feeding the flock.
Something tells me that the man who watches over the flock should be devoted to making the flock grow healthy, and not looking to harvest the young ladies that are under his care for his own use.
Could be I guess, but it kind of seems like a stretch to me. It doesn’t seem to be part of any leadership theme in scripture. G-d didn’t hold anyone in the Old Testament to that restriction, not even Himself, figuratively. If that is what Paul is saying, it’s a new concept, given with no explanation or examples given to explain why. If instead, Paul means “one wife” as a minimum requirement, with the reason given of ruling his own house well, it makes perfect sense. If the plain sense, makes sense, any other sense is nonsense... or something like that