Because it would just get lost in the noise of all the million other apps trying to grab your attention. Rather than sending yet another email, they should start filtering out the noise from everyone else to highlight the stuff that actually matters.
Hide the notifications from uber which are just adverts and leave the one from your friend sending you a message on the lock screen.
I meant in your inbox, not notifications on the phone.
Gmail already does filter the noise through "Categories" (Social, Updates, Forums, Promotions). I've turned them off as I'm pretty good about unsubscribing from junk and don't get a ton of email. However, they could place an alert at the top of your inbox to your "daily report" or whatever. Just as they have started to put an alert on incoming deliveries (ex. Amazon orders). You can then just dismiss it, so perhaps it's not an email so much as a "message" or something.
Hide the notifications from uber which are just adverts and leave the one from your friend sending you a message on the lock screen.