Just to interject, minions didn't do the same damage as full creatures. And really, at a certain point, shouldn't regular goblins be able to be dispatched in one hit?
Maybe because I'm old, I never had a problem with minions- when I started playing the game, Kobolds had 1-4 hit points, and Fighters got 1 attack per level against such creatures, so I never had an expectation that a horde of them would remain dangerous at higher levels.
If anything, the fact that you stopped encountering weaker creatures at a certain point was the weird thing to me in those days.
Now, if you want to keep using goblins, kobolds, or what have you at higher levels, and make them credible threats, sure, making level 20 goblins might seem odd. But at the same time, keeping Goblins relevant threats to level 20 characters seems just as odd- these are characters capable of tangling with ancient dragons, powerful extraplanar beings, and liches- shouldn't they be above goblins at that point?