A while ago there were a few labs in China in top 10 and they all attracted sanctions / bad attention. Now no Chinese lab report any data now
The basis for the ranking was a cumulative tracking of benchmark results that were required as part of commissioning bespoke computers. A contract would be written to buy a computer that could achieve a certain performance in operations per second, and in order to satisfy that the benchmarks were agreed to and codified in the contracts. Government contracts are to a certain extent public information so the goals and clout of successive performance were tracked in this way.
If you don’t need to satisfy a government contract, or don’t need the clout to attract engineers or funding, submitting results draws unwanted attention to what you’re cooking up.
Keep in mind the average hyperscalers cloud is not a particularly good setup for the top500. HPC tends towards more bandwidth, lower latency, and no virtualization.