I, for one, don't really think about ending counts, basically whatever feels doable at that time and reasonably diverse. That's probably the guiding line, but to be honest, I usually don't think about endings that much.
Though I'll admit that when you have an industry-standard plot layout, the girls are the point, then it's normal and even desirable to have 2-3 endings per girl. So they are tied to the characters, not really to the story, apart from the true endings sometimes.
Technically, Milk Swim had only one ending.
Kaori had 5, SoD had, well... 1 (or 4 with bad endings),... and Idol/TYPE, it had 2 (or 5, with bad endings). But anyway, it's an interesting observation.