Also, online banking has been a thing for so long on PCs which never had that kind of remote attestation. I also do not believe the security argument, but I believe that the banks believe it.

I suspect the banks want to do checkbox-based compliance with regulators and insurers without any deep understanding of the underlying issues.

Online banking doesn't need remote attestation. Some additional locked down hardware with its own minimal display is enough. My banks force me to use devices like those made by Kobil or ReinerSCT.