[levifig]

No need for tinfoil hats. This is a very basic networking consideration: peering. I've worked at ISPs and we would see traffic struggle through some of our contracted peers but not others all the time. It would take a while for all routes to update, and that if we had rerouting setup properly (not always the case). It gets extra complicated when you add BGP to the mix.

Long story short, most ISPs run or are well peered to data centers nearby, which is where speed tests are normally hosted at. For traffic outside of those hops, peering issues can lead to a multitude of issues... and you don't have to be evil for that to happen. No ISPs control the entire IP path between the client and server (with extremely narrow coincidental exceptions).