They got the good sitcoms on the air in the first place, didn't they? It's a company, and they look for profits. Bender couldn't push sandalwood, and Futurama couldn't hold an audience in a shitty timeslot without advertisement... the world goes 'round. Thank goodness people came to their senses.
Originally posted by PMD:
We didn't find out that Leela was a mutant till Season 4 (Production Order) so that should be left out anyway.
Maybe you didn't know until then... but the internet community had guessed it by season 2. Watch the episode I Second That Emotion
; specifically look in the background when Leela, Fry, and Bender are with the mutants right around when they hear about El Chuba Nibre.
But you're right, to the undiscerning eye, the revelation of Leela's mysterious past doesn't come about until later on in the series, so we shouldn't spoil that fact to newcomers.