Well, it's only a simple guess. For me, it seems like there are just certain shows/sitcoms/series that were great at first, but went on far too long that it should have.
A personal example for me: I thought the beginning two seasons of The Office(US) were great, but now, it's just gotten pathetically bad.
I'm not saying FM is bad, I think it's hilarious. I guess what I'm saying is, I'd rather remember it on that note .
But what you said is true as well, after all, nothing ventured nothing gained.