Well, that´s the point.
One thing about reactions is that in the TT D&D5e game you can choose to take your reaction or not, or to whom you want to react. That´s logical because you only have one per turn.
Maybe you want to use your shield against the ogre´s greatclub bash, not against the goblin´s knife stab. Perhaps you want to use your AoO against the mage that flees, not against the armored knight. Maybe you do not even want to spend your spell slot in it this turn.
sounds like the perfect kind of thing for RTwP; when it's available, you can choose to pause to use it.
