Part of it was because he was overtly commercial in an era when it was considered declasse'...
Part of it was because his early shortboard surfing held on to the longboard ethos...meaning he focused on sweeping pivot turns off the tailblock, walking the nose, etc etc.
And part of it was because his Hobie Mini Model didn't truly break new ground, being a shortened longboard for all intents and purposes.
That said, he was the earliest Californian to publicly embrace shorter boards. The first Corky Carroll Mini Models were out in 1967...and just co-opting the word "Mini" for surfing was a coup, given the popular mainstream use of the word at the time.
The early Minis were mostly in the 9 foot range -- presumably drawing off of Nat Young's 9'4'' World Contest board from the previous summer. Not a radical change, but a step forward.
The 'Super Minis' that followed dropped down into the 7 foot range, but they weren't especially good boards. (Hobie head shaper Terry Martin said Corky was the only surfer who could make them work.)
Most of the media coverage of Carroll in the late 60's was in and around the small wave California contest scene...but as you can see from these two shots, he rode the shit out of transition era boards when facing a 'real' wave.
What's gives Corky Carroll's legacy weight is the surf stoke he carried from of his career as a professional surfer into his "elder spokesman" phase...which is now entering it's 5th decade! First and foremost he was a surfer, and he's remained in that mindset through all the subsequent years and eras.
His regular articles in the OC Register are grounded in a waterman's perspective, and worth a read even if you don't relate to his talking points.
Here's the evolution of the Hobie Corky Carroll Models...from conventional board, to stringerless longboard, to early shortboard, to super shortboard. Roughly 1965 through 1968.