OK, I'll bite. First the disclaimer, I have a seven year old daughter, so watching this show is out of necessity.
I liken the premise to Giligan's Island. But, in this case, a family trying to get out of this time period (instead of off an island) and coping with the here and now in the meantime. You can only take that joke so far. So, what seems to have happened is that the show has morphed into much more of a teens dealing with teen issues show. Then, jump the shark with that cave man guy, and you have the writing on the wall for cancellation.