First those leaks have to be actual leaks and not one of the made up stories that the press (MEN) publish based on a post on the caf or reddit. And there is a fine line between high intensity and recklessness, it's not a good idea to train at a high intensity all season long because it is going to provoke stress and fatigue injuries, it will also affect the ability to repeat efforts when it matters, essentially during games, late in games or late during the season. Rest is part of training, managing fatigue and adapting intensity during the course of the season is also important.
As a basic example teams that intend to play deep into the season will generally build a conditioning program that is meant to see them peak around the final third of the season which is done by lighter conditioning at first and then you crank up in the middle first and then go down again in order to not empty the tanks; you build your fitness during the course of the season and do some maintenance at the end.
Now outside of some exceptions players aren't lazy and they aren't dumb either, they know and feel the risks of improper physical training, it creates fatigue which can't be avoided, it creates injuries and form irregularity.