Some issues could be prevented if push messages added end-to-end encryption by default, something that shouldn’t be particularly hard to use if it was built into the dev tooling. Instead, developer recommendations like this one [0] suggest that you should put content into your push messages and optionally use a separate library to encrypt them. Clearly developers aren’t doing this, hence the opportunity for surveillance.
[0] https://android-developers.googleblog.com/2018/09/notifying-...