Consider that if I know how to get to my bank's website, and it gives me an APK to install, I know it came from my bank, unless my bank's server is compromised in some way.

I have no way to easily determine that an app on the Play Store actually came from my bank. At best, I can look at the install count, hope the app store does a half way decent job looking for fraud, and hope for the best. Maybe if I'm lucky they have some sort of verification program?

The idea we actually trust app stores from Google or Apple over a direct install from the institutions we want to interact with is hilarious, especially considering all of the rampant malware and fraud issues on the Play Store.