Motorcycle helmets are relatively big. Any worth buying will cover your entire head, including your face and eyes. The good ones will even extend down and squeeze your neck to create a good seal. This is good when riding a motorcycle because it makes for a quieter helmet. But for sports this means that your head is trapped in this almost air-tight hot box. Of course this affects motorcycle racers as well, but they've got the benefit of > 100 km/h winds entering the air channels and cooling them. Hockey players don't.

Motorcycle helmets are also considered one-and-done deals. (although this is heavily debated within the community) They've got a great, thick layer of impact absorbing material, but once that material has been hit, it loses its effectiveness.

TLDR: motorcycle helmets are bulky, heavy, and are designed to cover the user in a way that's detrimental to playing hockey. Playing a physical sport in one would be horrible. And their materials may not be suited for the use.