Allan Girdler, of Cycle World fame with his iron motor XR 750 at Daytona in the 90's. I raced against him several times with a 750 Ducati.
The last time I talked with him , he said he was done with AHRMA because they changed the rules saying all bikes in F-750 had to run twin front discs and a fairing. He said his bike was never equiped with twin discs or a fairing ,though other versions on the 750 were , so he was out.
To me it's just another case of AHRMA throwing the baby out with the bath water.