Once you have a good amount of users testing, its not that difficult to get free servers from the ISPs. The secret is that on-net servers show testers better performance than off-net so every ISP wants to contribute the speed test server. If they dont do it they are shooting themselves in the foot by routing their traffic to competitor networks and getting test results behind their peers.

Whats even worst then your competitors can claim awards for the Fastest ISP and your marketing people are furious!

That was a persistent conversation with ISPs when I was building a white label WiFi product (competitor to Eero).

Some ISPs wanted us to pin to their servers in our app to have the best possible results (we refused) while others wanted us to use their servers because they offered 10G service and none of the other servers had that much throughout. So their true 10G line would be limited by the server, not the line.

Sure, but it's still a huge effort to set up all those partnerships and keep them alive. ISPs are often traditional and slow moving companies, it probably takes a lot of work to get those servers in place at the right locations.