Comment by faust201

Well summarised.

Another point is (often )the apps that banks makes are 3rd party developed by outsourcing (even if within the same developed country). If someone uses some MiTM or logcat to see some traffic and publishes it then banks get bad publicity. So to prevent this the banks, devs tell anything that is not normal (i.e) non-stock ROM is bad.

FOSS is also something many app-based software devs don't like on their products. While people in cloud, infra like it the app devs like these tools while developing or building a company but not when making end resulting apps.