I don't know the reality, but my guess would be that it's the inverse of what you proposed; a significant portion of fraud cases identified by banks involved a rooted phone. From the defender's perspective, this could be a problem they run into over and over again, and take an outside place in their eyes.

I think the point is that phone apps are more secure than, for example, web apps.

Users that try to use mobile apps as if they were web apps, disabling location, and security features are just flagged by numerous security mechanisms.

Probably. I know a guy who roots phones for older people or friends parents, installs pirated games and such for them and making sure it is locked down in certain ways for the older generation.

In other words, the correlation is that older people are more likely to have a rooted phone and are more susceptible to fraud.

Dunno how widespread this is, just something to keep in mind.

Perhaps people who unknowingly bought a rooted phone. I don't know how frequent this is, but it would be the only case it would matter.