So literally all ISPs then. Every one of those speed test sites are rigged. They seek the closest node, and, ISPs are obviously incentivized to run such nodes specifically because of that "closest node" fact.

That being said, theres a lot of factors that get your final speed result. A lot of your system resources will limit you long before you reach your advertised speeds (and this is assuming not even an internet, but lan connection). Compound those with things like routers outside your ISP, and toward the target, can be congested, or generally slow, and you will likely not even reach 10% of advertised with a single system.

Obviously nerds and power users might get more out, but its really pretty rare.

Those testing sites are just a general tool for troubleshooting, and even ISPs should not be relying on them to determine speeds.

If you want a proper speed test look for "(size) test bin download" and youll find sites like HE.net with 500MB-10GB files that you can direct download and gauge your speed with. While they are effectively what the speedtest sites do, they are a much better gauge in my experience