It actually makes sense as a business model, but they messed up by backstabbing their first customer (after contracting with OnePlus, they signed an exclusive contract with MicroMax that no other company can sell cyanogenos in India, which, had OnePlus not made OxygenOS, would have killed them.)
It was probably the stupidest move they could have done, as no company would trust them again, and lost them all the goodwill they had.