I tried to book a rental thru CCC for next year and the only option was Enterprise RAC. When I was there earlier this year it was only Alamo and National. FYIW it wasn't cheap.
Can't answer your specific question. However both Alamo and National are both owned by Enterprise. They are probably consolidating some operational aspects, much like the did at airports several years ago.
I won't bore you with the historical target markets that Enterprise, Alamo, and National used before the consolidation of the rental car market.