GM produces their own Ultium cells, but the partnership was mainly for the rest of the vehicle. (Control systems, etc, etc) so they could slap a Honda infotainment system into it and a different set of sheet metal on it and say they’ve got an ev in their fleet for tax and fleet fuel efficiency reasons.

My insight to why is limited to what seemed like a tradeeoff where GM got info on how Hondas hydrogen powered research and development and in return GM shared theirs for batteries. A large percentage or engineers in Detroit are not sold on EVs, especially for things bigger than cars, or applications requiring more power density. If it wasn’t for government essentially forcing them to start transitioning to EVs, most of them wouldn’t be.