The receiver's email and the app are enough to send Bitcoin. So it's different from other services and wallets.
no it is not different from other "services" because it already exists and it is called PayPal. since when using a centralized service in control of your funds, you are not longer sending "bitcoin" you are instead sending IOUs.
Exactly. Getting one's bitcoin by just receiving an email can be an attractive of an idea. I am sure there had been those who think of this before and concluded that this is not what the cryptocurrency marketplace wanted anyway. There is no other way to do it but follow the centralized system like what PayPal is doing and offering. Though I don't see that much wrong with PayPal as it has a big role to play with the market it is dominating, if the same can be copied then it can just be a big waste of time.