Why dont most boxers pivot the foot/leg all the way in?

[BCBUD]

I'm only 16 and a newbie at that. However my old coach said that in the olden days fighters were taught to throw there all into a punch. Today it's all about short and quick combos best thrown from the front foot, besides most gyms here in Montana and alberta don't want a follow through on the hook, most don't even want a right hand behind it because they want it pasted to the chin. It's all about short double hooks counters off the straight right to the face. Try and find a gym in Montana and alberta that doesn't fight off the front foot I doubt that many exist, I know that because of the tourneyments and there's only 1 competing gym in alberta that I can say fights off the back foot although many may say that they do.