Because they aren't. Teams, by definition, are as good as their record. That's why they keep score and keep track of wins and losses. Fans of teams with (long time) losing records generally say this if their team shows any signs of life during the season. Or at the very least to give themselves and each other hope for the next season.
I'm not a big believer in "attitude" or "effort" being a determining factor. Attitude, in my opinion, is just bull **** right up there with "buying into a system". These people are professionals getting paid obscene (in a lot of cases) amounts of money to play a freaking game. If they cannot, or do not, give their best effort every game, then they should be fired and no longer be professionals.
Just my opinion of course. Not trying to bicker with anyone.