I'm talking about the security model of the platform, not the way you use your devices. If you do your online banking in a browser on your computer and your system gets infected with malware, that malware can access all the files on your computer. Including application data of your browser. It can access your cookies, which your bank's website uses to store your login information. Such an attack is impossible on a mobile device, since apps can only access their own data, and inter-process communication is heavily restricted. Additionally, mobile operating systems like Android have complex permission systems, as well as kernel-based mandatory access control like SELinux/SE for Android. Your typical desktop OS has none of that. Android also has a strong implementation of Verified Boot, which makes sure that malware can't persist on your system partition, even after your device gets infected. I recommend this video if you want to learn more about mobile device security: https://youtu.be/yTeAFoQnQPo