Oofta
Legend
... Because 5th edition doesn't actually support play beyond around 10th level. (And is barely functional from 1-10 to be honest.)
I would disagree with that, I've run and played in a couple of campaigns now that got to 20th. If the campaign isn't working at higher levels I'd say it's a problem with the DM, not the game.
It's more difficult to run higher level games and you have to do more to challenge characters at higher levels. I'm not even saying it's worth the effort for everyone.
But it works reasonably well, certainly better than 3.5 and previous versions.