I would guess they wanted to make sure they're reading the rules right and didn't miss anything. Other people chiming in with houserules are just sort of tangential, and the ones arguing that the initial reading is incorrect by RAW aren't making a good case (in OP's opinion) for why it isn't.
At least, that's what the context would be if I posted a question like OP's - it's intended as a check on the reading, not a survey of houserules or a debate about how well the rule is written in the first place.
The latter being a perfectly normal derailment of the thread around here, but that can be interesting by itself. I agree it feels cheesy to have nearly continuous advantage from an invisible imp, both narratively (how many effective invisible pranks can it really pull off?) and given the number of monsters who couldn't easily deal with it, (unless they're spellcasters) but I also agree it's legal if you want to stick to the books / a houserule to not allow it.