Why does Riot have minion block in the game?

There was the discussion around crit chance being inherently RNG and forcing the game to be lop-sided with some adc's criting 5 autos in a row whereas the opposing adc doesn't land one crit. Personally, I don't mind crit chance, it's a gamble. However, minion block seems entirely pointless as you can get caught to where you can't move and someone may not, and it's not down to a chance of whether or not you get stuck, it just happens.

TLDR: Minion block is unhealthy, why is it in the game?[zombie-brand-mindblown]