You have to connect thousands of cables, have hundreds of nodes, with thousands of components, everything interconnected, and if you connect one wrong, the computer outputs incorrect results. You have to routinely update the software, and if a software upgrade introduces a 20% perf regression (which happens), then your 10 MWh cluster starts burning 2MWh for nothing. Or maybe your cooling system sucks, and after a minute of running at full capacity, you need to throttle your cluster to 0.1% of the peak to keep it cool enough that it runs "something".
That's why all systems in the top500 i've been involved with (15 or so) run these benchmarks as an integration tests on every single cluster maintenance (node updates, servicing, OS updates, etc.).
Submitting these results to the Top500 costs you nothing... if your cluster actually works. When you submit to the Top500, they ask for access so that they can re-run them themselves, which happens typically during / after the next maintenance to avoid impacting any users.
If they haven't submitted, 100% sure their cluster does not deliver what they say it should deliver on paper. Maybe it delivers 1% of it, or 0.01% of it (seen both cases in real life). If they haven't fixed it, then maybe it can't be fixed.
HPL, MLPerf, Spec, Stream, OSU.... these are not "benchmarks for bragging rights", these are tests that show that your system works.