That's true for browsers, but Google controls both the Android OS and Google Play Services, giving them access to hardware identifiers on Android smartphones. Given the broad adoption of Android devices and the potential to correlate data, this is not a case of "making stuff up." Even if your MAC address is spoofed/randomized, the remaining data points are still sufficient to track you.

Doesn't make sense to track and correlate the mutable MAC address when you have access to the burnt-in device serial number and IMEI.