Because the Rattlesnake had a long history as a political symbol for the unity of the thirteen colonies and was meant to serve as an example of the revolutionary ideals.

Gadsen himself was a staunch supporter of John Adams (though he was, paradoxically an enthusiastic eslavist) and he spent time in prison during the war as he couldn’t give his word to a “false system”.

Sadly, the right has been misappropriating revolutionary symbols and that’s what I meant as unfair.