is there a reason to play an immobile tank

when you can play a mobile one like fizz or ekko. I mean lets be honest here. how many times you have 250+ armor and 200 MR with 3.5k health and you die in 2-3 seconds because you can't get the enemy off you? i mean i feel like for ekko. damage isn't the only thing. its the least thing. the cc and the mobility. allows him to be such a good tank that just doesn't sit there and die eventually. he can go straight for the adc with absolutely no way to peel him.