The obvious answer is that "non-profit" doesn't have a meaningful definition outside of the tax code. "Profit" is an accounting trick, for one, so any "excess money" (the commonly-understood meaning of "profit") can easily be funneled into grants, administrator salaries, larger workforces to satisfy administrators' urge to play primate dominance games, etc.

Another one is that "non-profits" (in the tax-code sense) are actually allowed to make a profit (both in the accountants' sense of the word, and the ordinary sense). Hospital systems, for example, often make huge profits, while hiding behind a non-profit status that they've inherited from the bunch of actually-charitable nuns who started running the hospital 150 years ago.