Because some banks now require you to authenticate every payment (eg. online payments using your debit card) and every new recipient for bank transfers, using their phone app. The apps rely on the chain of trust that Google and Apple provide with their TPM or "secure enclave" chips to cryptographically authenticate that it is indeed the same device that the bank previously authorized.

Online banking via the website of these banks will still require at least one tap on the phone app to authorize any transfers that you make on the website.

Linux phones (and custom Android ROMs) don't benefit from this same chain of trust, and so even if they have the secure chip in the hardware, the banking apps don't have a convenient API to query it, so the banking apps just don't work.

Banking fraud causes a serious amount of money lost to criminals each year so it's not surprising that the banks want better ways of determining if a request is really coming from their customer('s device) and not a criminal who phished their online banking password.

This situation won't change unless either Linux phones gain in popularity enough that the banks decide to port their apps to the platform or a law is passed saying that banks must support more than just Google and Apple (ie. custom roms etc.) at which point the work will be done to use the hardware attestation available in the phone on other software platforms.

In my country we have an phone number based instant money transfer protocol called Bizum, everyone uses it. When you go out eating, one pays with your phone via NFC then everyone bizums the payer with their part. It's something I use almost every time I go out.

Bizum is a protocol that's implemented in the app of the banks themselves, so I kinda do need the app, I'm not going to go into the phone browser to go into the app web to do a transfer of 14.5€ that will then shocker ask me to verify the transfer via the app. Even if the verification was a SMS nonce code that would be incredibly annoying compared to what we already have.

So yeah, people are hung up on banking apps because they kinda do need them with them.

The main use of the apps is 2fa. There are other things that are also becoming harder without apps, like public transport.

The apps might even work for now, but then I'd rely on Google not pushing some bullshit that breaks it.

My bank has "removed" the mobile version of the banking website. It's technically still there, so it can still be used, but you need to know the full address for it or keep it bookmarked. The main page's link to the mobile banking page now takes you to another page that tells you it no longer exists and to use the app instead.