A Tiers have been limited for at least the past few years. IMO it is ridiculous. If they want fewer they should raise the standards. It's not like they have any A Tier "brand" they are protecting at this point nor does the PDGA provide any support to them beyond what is provided a C Tier.
I believe the point is to protect the investment made by the TD. If you scrape together sponsors for the requisite added cash and then someone else throws an A tier down the street you would be splitting the player base and your efforts would be wasted.