[there]

You can encrypt notifications that go through Google's FCM and Apple's APNS push notification servers. This is how Pushover works - each notification is encrypted with a device-specific key, sent through the notification servers as an encrypted blob, then the app on the device is woken up and receives the blob, decrypts it, and posts it as a normal notification.

[wybiral]

You could. But if you don't need that kind of added complexity and scale (and I don't for personal news updates or IoT device alerts) then why jump through those hoops?