They are probably not responding because it is getting into an area where they would be exposing their business plans and possibly trade secrets to their competitors.
It would surely put them at a competitive disadvantage if they publicly stated they don't have a system in place to evaluate and monitor each individual towing company. Their competitors would point out that public statement while surfing around the fact they don't have a system either. Kind of like a politician saying their opponent doesn't have a viable plan to bring peace to the Middle East or lower the cost of healthcare.
Most areas of the country only have one tow company capable of handling many of today's RVs. Some areas don't have any, and that requires finding a provider who is potentially a hundred or more miles away. When there is only one, what good does vetting do?. They sure aren't going to X out the only provider even remotely capable of responding.