Why does Google FRP even exist?!

For everyone who doesn't know what FRP is: FRP (Factory Reset Protection) is a partition on an Android device that stores data about the last used Google account on the device. It "protects" the device to be used by a second person (or a thief) even AFTER a factory reset when executed via bootloader.

Last week I bought a HTC One A9 second-hand w/o any documents. I ensured it has been reset, so I took it home... I then wanted to set it up, as following message appeared on the screen: "This device has been reset. Please login using a Google account that has been synced with this device before."
I checked the IMEI for being blacklisted, but it wasn't. Unlocking the bootloader and erasing the frp partition is not an option, because on HTC devices you have to enable OEM unlocking in the settings first. Someone stated on a forum, that you can bypass the bootloader lock with a "RUU Image" (I'm not familiar with this so pls don't blame me for that statement). But since the phone has a branding from Vodafone Germany, I can't find a RUU Image that would flash the device without a CID mismatch...

Why the f*** does Google have to implement a feature that prevents to use the phone when bought from another person that you don't know?

I just learned about FRP (Factory Reset Protection) yesterday.
Didn't know that was a thing and while it's annoying it's also quite clever.