In the traditional model, the anime is marketing material for the franchise. Money is in figures, merchandise, and manga, which usually all existed before the anime was created. Generally only established studios with plenty of funds do original (not first portrayed in another medium) anime.

OPM went to JC for S2 because the very expensive S1 from Madhouse had already satisfied the goal of bringing tons of new fans to the franchise.

This is changing though, as anime is getting cheaper to produce and international viewers are increasing.