> My grandma should not have root on her phone and a lot of younger people as well.

I would agree.

> Making it easy to root phone makes it easy for scammers to ask people to unlock it.

I would also agree, so then: don't make it easy.

> Mobile banking apps refuse to run on rooted phones.

... but they do run on my web browser. On a computer using open-source software without even secure boot enabled. So, it seems to me this is a cop-out by said banks. They shouldn't require client-side absolute trust to run, and evidently they actually, practically, today, do not require that. It's simply a choice they made, presumably out of laziness or greed.