Because the stupid dumb of dumb don is obtuse and oblivious to his own yards and miles and acres of slurred words mispronounced words and words that don't exist except in his muddled addled brain.
He attacks insults Joe Biden for how Joe speaks.
Dumb don is really dumb doing that because all the late-night comedians and all the dumb don enemies are having so much fun showing how idiotic and jumbly mumbly dumb don speak is. It's a RIOT! Attacking Joe Biden for messing up a word here and there and we get a refresher EVERY DAY of the extent which the idiot man dumb don is a bazillion times worse. Proof he isn't normal. Too funny in a tragically sad way isn't it?