I came here to say that a significant number of developers want apps, too. Including me. For many reasons including performance. But the one I want to mention here is security, because it
systematically gets missed by web people:
End-to-end encryption fundamentally doesn't work in webpages. Because when you load a webpage, you have a 1:1 connection to the server which sends you the code you need to run. You have to trust that the server sends you the right code, every single time, and there is no practical way to verify it. The whole point of E2EE is that you don't trust the server, and with a webpage you fundamentally trust the server. That's completely incompatible.
Let's compare the Signal mobile app and the ProtonMail website:
- With Signal, you can audit the sources, compile them and run that. You know you are running the code you audited. You can trust someone else to audit the code, compile it and run it. Or you can just download it through the Play Store and know that tens (hundreds?) of millions of people did that too. If you download it through the Play Store, you can "verify" your app with someone else, making sure that Google didn't send you a modified version (which would have required Signal and Google to collude in the first place). You know when the app is updated. If it matters for your life, you can make sure you benefit from end-to-end encryption.
- With ProtonMail, you load a website. Everytime you load it, the sources could change. When you enter your password, you enter it in that very code that the server just sent you. So the server could identify you, and just this one time, send you a different version of the code, just for you, that would leak your password to them. You don't have any way to pin a version of the website and compare it with others, and there is no need for Proton to collude with anyone else to do that (it's a lot easier when no collusion is needed).
Again: end-to-end encryption fundamentally does not work with webpages.