I don't think this is actually happening. There is an enormous loss to scams mostly by tech illiterate people using the preinstalled operating system. I don't think the losses that involve user installed OSes are in any way significant.

I think it has more to do with the phone being tied to an individual, the banking and spending activities being tied to the phone, and the government having some hardware attestation about how people are spending their money and with whom. If you root a phone, you can change things like the MAC addresses. You may be able to futz with a softSIM/eSIM. That makes you harder to track.