The rules of English state that once you stick a couple words together with a hyphen for a long enough time, those hyphenated words later become a compound word without a hyphen, and thus "correct English"; and the amount of time before you're allowed to remove the hyphen is completely arbitrary, but until it becomes official, everyone will tell you you're doing it wrong.
Then you'll show them that it made it to the dictionary, and they'll get mad about it not being "proper English."
Ha! Like that's a thing.