There are a lot of TB games you react in the enemy`s turn, like "The last remnant" "Armello" "Jhon Dever´s Lone wolf" etc
In those games there are several mechanics that show you can make reactions in the enemy´s turn without compromising the animation nor the pace of the combat.
I will say it again: You only have one reaction per turn. You do not want to waste it.
Also, only for Attacks of opportunity (that´s only a reaction out of 15-25) you usually have the option to choose if you hit or not, what enemy do you hit if there are several opportunities to do so (You may want to try to hit the hurt shaman that flees or the enemy that charges your squishy wizard instead of the damage-resistant earth elemental that comes first)
You may use (depending on class and feats) your attack of opportunity when an enemy enters your "killing area" instead of fleeing, users of "War Caster" feat may choose if they use a spell or a melee attack to deliver your attack of opportunity. So maybe you want to use a spell instead of your mace to attack that damage-resistant elemental.
That would be a hell of a lot of automated choices to make. And that´s only one reaction, one of the simplest. If you do not have all this choices to react against the action of the enemy instead of being a psychic that have to divine what the enemy is gonna do and put the levers on accordingly beorehand; I do not know how that´s "give more control to the player" instead of narrow down your options to a few general all-purpose on-off reactions you set just-in-case.
You do not need to be a D&D hardcore player or whatever to want a game where you have more accurate ways of dealing with your enemy or more options for different builds and you do not want easily exploitable quirks just because you know reactions are automated so they´re always against the first attack and you can use it in your benefit.
