The motivation is pretty weak. If people found a way to make money by doing this, it would be massively exploited. But the reward for breaking a bunch of phones is... self satisfaction? ok.
I don't know that people were seriously making money on most of the script kiddie shit that was going on on the internet back before ransomware and bitcoin and such (other than AV vendors), and yet it was rampant anyway. I imagine there are still people out there who do this sort of thing "for the lulz".
I'm not so sure. Nowadays they can focus their energies on profitable activities like ransomware or adware. If you're going to break the law to cause grief anyway, why not make some money while you're at it?