I don't disagree with owning your hardware. I'm saying that a regulatory body can pose rules on where critical software can run. Part of this is data exposure: A banking app running in a tampered environment makes some malwares possible, which is the side you want an "I know what I'm doing"-button for. But it also creates risk for the bank. In letting you look into network-traffic and memory-dumps, you may discover ways to manipulate an unrooted instance or the backend server. This is security through obscurity and I'd much rather have everything open-source, but it's what we're dealing with.
On the other hand, the bank promises to cover damages, whenever they do mess up. You could give them an easy excuse by taking on that responsibility. But regulations don't allow that, much like they don't allow you to do your own high-voltage, high-current electricity. And frown upon you breaking load-bearing walls in a housing complex to have a more open kitchen. There is a line where "let me do what I want" becomes anarchy.
Now bringing DRM into this, misses the point. There is telemetry in these apps. But there is no piracy or copyright infringement to be had. The bank doesn't fear you giving yourself a million dollars by changing your balance in memory. It's all about responsibility in case something goes south. They would love to shift it all onto you, but they're not allowed to do that. Attestation was never about protecting you, it's about protecting them from being blamed.
There is a bunch of parties making guarantees and complying with rulesets. Domino-ing all of them would make you extremely vulnerable. Which is why I opted for "tamper-proof containers running in a unproven host", rather than signing an unlimited waiver.
A thing that popped up in corporate space is IgelOS. It's an immutable image meant for linking to a VM workstation on a company network. Seems worth checking out.