I think its sort of a boycott from the top pros. USDGC had as much prestige as Worlds. Its the tournament made for the tip-top level of Disc Golf. Worlds invitation criteria is so much easier to meet. To even qualify for the USDGC was a great accomplishment before, but now you won't be considered the best of the best.
In my opinion there is a place for handicapped competition but taking the most prestigious tournament in our sport and making it handicapped is/was not wise.