TINKERTOOL APP

The vendor has the reason right on their own site:

Anything on the App Store has to abide by certain rules to be there. One is they do not attempt to modify other apps. TinkerTool's entire reason to exist is to modify the behavior of the OS.

OnyX isn't available on the App Store for the same reason.

It doesn't mean either is bad, or intentionally malicious. It only means what they do automatically excludes their ability to be on the App Store.

It may be that something in the app violates Apple's security or some other term. Sometimes an app my report on its own site why they have decided not to make an app available on the Mac App Store.