How do you re-do something that depended so much on the talents and charisma of its cast members?
It’s a tricky one, isn’t it. On the one hand, successful older shows were often lightning in a bottle; on the other we’re basically saying “there are no good actors any more.”
Battlestar Galactica is probably a good example here. I remember when they first announced a reboot and the bottom half of the Internet melted. Recasting Dirk Benedict’s iconic Starbuck as a woman? You’ve ruined my childhood, etc etc. As it turned out, it was really good. (OK, the ending was abject twaddle, but here we are.)
Fresh Prince though… I dunno, when you think about it the premise is pretty thin. Street kid goes to live with rich family and… uh, that’s it. That’s not a lot to hang your hat on for a reboot. As you say, it was basically a vehicle for Will Smith to be Will Smith.