Except there are so many things coded as minions. Minions as a whole group would be recoded, meaning everything that took properties from the minion class to function would have to be recoded as well. On top of this melees are actually balanced around minion block.
I personally am also a big supporter of minion block. It adds a lot to trading, especially as melee champions. Moving in when your enemy is in a bad situation, approaching from a good angle yourself, knowing how minions move around in fights. All that is lost by removing minion block. Suddenly it doesn't matter when a jungler ganks. Currently you can wait for them to be hitting minions and therefore have minions behind them. It rewards intelligent play on the part of a jungler. However by removing minion block one can just path in a straight line to their turrets.
There are a lot of neat tricks you can do with minion block. Sure it bugs out and you get stuck from time to time. That sucks. However I don't think it is worth removing all the interactions it offers just for that. Most of the time when you get screwed by minion block it was your own fault and something you could have played around better. Most of the time if you take the time to pay attention and learn from it you can learn and improve, eventually using minion block as another mechanic to control your opponents.
It is only on the rare occasions it truly locks you in place that it is actually a negative impact, and there are a number of ways to avoid that too.
