There was a guy in the 1800s names Crocker Jacques (of French heritage)who apparently was a good fellow, an accomplished hunter and outdoorsman – sort of a Paul Bunyan kind of guy but from up in northern NY State not far from Canada. (His real was Crocker Jacques Dubois, but his friends shortened it because it sounded better).
Anyway, his name was pronounced Crocker Jock – in other words, they shortened and anglicized his last name.
About that time (roughly 1874–1875) the Bike company first manufactured the Jock Strap (see the following wikipedia. Those were called Jocks.
So Crocker Jacques didn’t like being confused with jock straps, and since he wasn’t going to convince corporate America to change, he decided to change his pronunciation to
Cracker Jack – as we know it today.
The bottom line is that a old time of French background had to change his name in order not to sound like a testicle holder.
Has nothing to do with being a cracker.