Why cannot I manually move the app to system?

Avast Mobile Apps Avast Anti-Theft for Android
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I saw the post about how Avast got rid of the root installer because they’d rather dump it than develop it, but Im not understanding why I can’t even manually move the anti theft app to system myself without the app launching a popup saying that since Avast was installed from Google Play, it cannot be run in “rooted mode” and for me to reinstall it as a user app.

It’s still the same app either way and being that I paid for it, I think I should have a say in where it’s installed on my device (Not to mention that the only reason I even chose Avast and bought a license for it was because it could be installed as a system app)

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I can't even manually move the anti theft app to system myself without the app launching a popup saying that since Avast was installed from Google Play, it cannot be run in "rooted mode"
That is easy to answer. It is not a version for rooted devices.
It's still the same app either way and being that I paid for it
No, it is not the same application. Hence why there was a normal version and one for rooted devices. A Toyota and a Ford are both cars, but they are not the same ;)