All these numbers are fake. They are all special cased in most ISPs with the cooperation of cloudflare, Netflix, OOkla, Akamai, Google, etc. The centralization of the internet around AWS, Azure, Google, Netflix, Cloudflare, etc has been a godsend to ISPs and the internet infrastructure in general. Maintaining good network conditions to 4 or 5 dozen networks and working with them closely is so so much easier than maintaining full peer-to-peer network conditions. Go ahead and try to test internet speed to your home network over a wireguard VPN and compare it to the performance of the same VPN when connecting to any of the major services. Try to setup a tunnel between your house and your friends house in the same city and test the speed and compare it to fast.com or cloudflare.com or speedtest.net

I had not heard of http://speed.cloudflare.com either. I just tried it and I did not get accurate numbers. wifiman.com, from Ubiquiti/Unifi team does provide more accurate numbers. fast.com numbers are pretty accurate as well.

The difference is that until now I had never heard of speed.cloudflare.com before. (I know about fast.com though.)