This cuts both ways - ADP requires changing some settings on-device, and (in some cases I've heard) calling Apple to disable. So it is baked in, but it's hardly easy to enable and disable

GrapheneOS (which, FWIW, I do trust at least as much as ADP) has a web-installer IIRC, making it similarly easy to enable, but a little harder to disable for normal users. Moreover, it's not built-in to the Pixel. It's entirely third-party, and did not ship on mass-market hardware

Being an option on the default OS, with OEM support, can make all the difference sometimes