Well, simple for one class. Not sure what all the other melee classes are supposed to do, lol. From what I've seen:
Rogues could disengage as a bonus action, but then they can't dual wield to ensure they get their Sneak Attack!
Monks could disengage as a bonus action, but then they run out of ki and can't attack more times!
Paladins could....uh....heal as a bonus action?
Rangers...wait, does anyone play melee Rangers?
And worst of all, the poor Barbarian, who despite what everyone seems to think, can't Rage in every fight, and whose natural armor won't be better than half-plate until he has +7 split between his Dex and Con scores. I guess he could tank his damage by using a shield?