Why is there a button for Attack of opportunity?
Why is there a jump button? If I want to jump somewhere, I can just click on where I want to go and the character should go there (auto roll check).
I agree with your questions to a large degree. But here you haven't thought it through.
Do you only jump as part of movement? No, you don't. You can use jump in combat, it's an Action. (Well Larian seems to think bonus action, they are wrong). So you need a button to actually perform the action of jumping, as opposed to just running somewhere.
Out of combat you might want to use jump to not run through things that can hurt you, like fires. You need a button so that you can choose when you want to jump, where it's not obvious that a jump should occur.
Lastly, you can jump to places that might hurt or kill you. Again, you need this to be an option, not automatic. I already hate the times my character does jump down roofs and take falling damage, when they were right next to a ladder!?
So yeah, there are ample reasons for having the button. But I agree, if there's no cost to the jump, and the only reason you are jumping is because Larian put a gap in the bridge, then it should be automatic.
As for Reactions. Reactions are a bit difficult to get right. I think I agree with you though, give us a pop up. But before they do that, we should really get the combat speed optimized. Right now combat is slow as hell, and a pop up every now and then would make it slower.
But I think the pop up is the only way to really implement reactions, and spells like Shield and Counterspell.