Sorry, semi-pro.
1) because we can successfully - you start brand new players who've never cued at a 12-14" bridge? - no you don't, no way.
2) to have a longer "sight" for aiming certain shots - you went on to post that you agreed with this point in principle - long bridge, better sighting (sounds like a Papa John's ad)
3) sometimes because we're too lazy to reach for a mechanical bridge or stance accurately - okay, pros are disclipined in this area not to be lazy
And, I will continue to contend that the average casual player or even reader of this forum likely has too long a bridge - and feel free to address the heart of the question that you raised yourself - WHY players used shorter bridges years ago - it's not just because they all stood upright - some of the oldie goldies got way the heck down there.
You're reminding me of the golf pro who says, "Watch and learn how to drive" and hits one 300 yards down the middle and now says, "You do it." You know it takes time and discipline for newer or less skilled players to lengthen their bridge more and more to break faster and more accurately. It takes a long time in some cases. But I guess everyone should use foot-long bridges in pool for most open shots because you or I might... the average player doesn't need to see better but stroke better - once they get their cue ball rolling straighter than can get lower and make a longer bridge (maybe) to do what you said.
I know I'm fighting against the current wave of reasoning among teachers. But everyone who is about a 7 APA or less whose bridge I've shortened has pocketed more balls immediately. Think about the angles a bit also - is it simpler to get the head and eyes closer to the ball with a longer or shorter bridge? We both know the shorter bridge (assumed at the table in a proper manner) brings their whole person a little closer to the action.
I doubt I'll reply to you on this again and sorry you hurt your head on your monitor. Maybe ask questions instead of assuming I'm wrong about everything and give me a chance to post further details...