It's because "security" is not a user one, but a security of Google Play Services.
As rooting may tamper the google's telemetry (can we already call it "spying" please).
There was a time when we did call it spying. Programs that had what we would now call telemetry used to be called spyware.
The term has fallen by the wayside and hardly ever gets used nowadays.
It's the security of the ecosystem, where the interests of app vendors are fundamental: content distributors can count on enforcing DRM, and banks are relying on the camera used for KYC actually being a camera and not a virtual device.
It's about keeping google's device secure *from* the user.
Just accept being spied on, it’s not as if there are genocidal billionaires out there.
Not to mention, play integrity is being used a some sort of "anti cheats" by bank apps and other essential services. Even some government apps in the EU, essentially forcing you to be spied on by google.
The worse part is that, you can do all of those functionality with a browser on linux (or Android), yet to use them as Android apps on a device without gapps (even if jt's not rooted and with locked bootloader) is not allowed. Make this make sense.