Why is the Apple Watch GPS so inaccurate for running?

I have used every version of the Apple Watch over the years, and tried all the various calibration tips suggested to improve accuracy. But still, my Apple Watch 6 is reliably inaccurate, always calculating distances 1-2% long (and therefore paces that are too fast). I just bought a Garmin Forerunner 745 which is amazingly accurate for pace, cadence, and distance, matches the Apple Watch for HR, but doesn’t have the cell phone, texting, or music capabilities of the Apple Watch. So now I wind up running with two watches, which can’t be the right answer in 2021. Why can’t Apple make a watch that has all these capabilities in one device?