Chop saw

Needed a new blade. Was near Harbor Freight when I remembered. 5 pack for 20 bucks or whatever it was. First few cuts went like a hot knife thru soft butter. Last cut....what the hell happened? 2.5" 3/16th" walled square stock. Couldn't get thru it. Cut 3 sides and just stopped cutting. Had to take the metal out and roll it 90* to get it to finish. How in the hell could a simple abrasive wheel not cut?