OEMs rarely make money: they get the design in but don't get significant payments until volume gets up (if ever). And once the original version is designed, the buyer wants to increase margin and/or lower costs, which they do by pressuring their suppliers.

Furthermore, ARM isn't even an OEM; it sells licenses (patent licenses plus rights to use copyrighted designs) so Oppo is paying someone to design a chip using ARM IP and paying someone else to fab it, and then a little goes to ARM.

All in all, a shitty business unless you get lucky, which ARM did. They took advantage of their luck, don't get me wrong, but luck was what gave them the opportunity that so many others either didn't get or didn't know how to take advantage of. Microsoft was another lucky winner who knew what to do; Intel went the other way and made their own luck until they got distracted.

Unlike, say, NVidia, Intel and Apple, ARM is not in control of its fate, or rather has limited control. And despite those first three having control, that doesn't guarantee anything: one of them lost the thread, one of them had a near death experience, and one of them has so far managed to stay on top.