That’s because a speed test automatically looks for the best hosting server with the lowest latency. That way you have less chance of ending up with a bottlenecked node. Distance doesn’t even matter that much. I just did two speed tests. First server was an hour drive from here, and was faster than a server just a few miles down the road. The data can only flow as fast as the slowest node in the route, and every single node has its own load to deal with.