Even if that's the reason, they could have greater gains if they promoted an altcoin instead, which is far more centralized and easier to manipulate. Even if they enforce their users to use it custodially, they don't have much to gain and they're against its purpose. Zoom out and see that the existence of it is against its purpose.

We shouldn't expect from the banks to spread the usage of bitcoin, it's ironic. Bitcoiners, remember your moto! Bitcoin = Liberty ≠ Subjugation = Banks!