Why do you think apps should verify their integrity in the first place? In the case of banking apps or other online apps, the APIs they use should be secure in the first place so a user can’t achieve anything meaningful by modifying API calls. In the case of offline games with monetization, a hacker who makes a pirated APK will also remove the restriction so legitimate players on non standart ROMs will get screwed. In the case of messaging apps with a “delete messages” or “one time view” function ie. Whatsapp, the sender shouldn’t take that their actions will be respected by other clients because modded apps exist and Whatsapp doesn’t care if you install it on a rooted device.