Hmmm...ok.
I guess myself and a couple of hundred kids who were there at multiple tracks were not racing.
This bike, along with other monoshocks were indeed raced.
BMX Hall of famer Thom Lund raced the Wayne King mono in the early years. Billy McIntyre raced his version of a monoshock well into the years when regular "hard tails" were already the norm.
And while the Yamaha moto bike was a dual shocker, it too was raced quite a bit until we realized it was too clumsy for BMX racer.
A quick look at BMX news, BX weekly and other literature of the time will verify that this, and similar bikes, were indeed raced back in 74 and 75.