Answer: because sometimes you're aiming to trip someone (maneuver) and can't bring that extra strength to bear, or you're fighting a mortal and don't want to just pancake them, or you just don't want quite as much risk of breaking your weapon... And sometimes you're fighting a martial arts master who makes a "Water Stance" fists maneuver, invokes it for effect, and suddenly your bonus from might is reducing your attack rolls instead of increasing them...
A lot of the time, yeah, if you've got might higher than fists/weapons (either through strength powers or just plain skill), you'll want to attack in a way that lets you get some use out of all that extra power. And sometimes doing that will backfire. If there's no chance of it ever backfiring, though - then that is, indeed, boring, and shouldn't be done.