Wny are these phones so popular with people that like to have a "de-googled" phone. Seems's counter intuitive to buy a phone made by google, but I don't know anything about anything .
Discussion
Because they're the most open phones out there. The Android Open Source Project is made to run on these devices. They're developer phones. So, naturally, developers build open source software for them since all of the source code and binaries are available for this hardware.
Because Pixel is the only one that is supported by GrapheneOS, and the hardware is great.
It's an effective androidOS phone because it can update androidOS longer than others & install grapheneOS.