There are a lot of security guarantees that go away with a rooted phone, and I wonder if "in the wild" more often rooted devices are malware than user rooted.

From the perspective of a company, these things boil down to numbers. They have the data, and they can review it. If they find a correlation like that they lost large numbers to rooted phone, they will ban it.

I have had email forwarders and @protonmail.com accounts get blocked only because they are more likely to be fraudulent and companies can just block because the hassle isn't worth it.