First not all Android versions do that, and not all vendors implement that. Not everyone is running the latest version and has a Google Pixel. Second passing from the OS is less secure since there are a multitude of actors, Google, the device vendor, eventual VPN app, etc. that could get access to that queries (in fact apps to block ADS such as ADAway if you don't have root use VPN functionality to intercept DNS queries). In the end if you want to be safe better not pass from the OS in the first place.

My Samsung phone is on android 9 (released 7 years go) and has DoH