There were curbs before 1970s, right? I wonder whether everyone had to dismount or dramatically slow down before curbs until bunny hop and wheel lift became popular, I guess, in 1970s among first BMXers. Same with cyclocross: for decades, from its beginnings, riders always dismounted before barriers. But suddenly, inspired by BMX, they realized it's possible to simply jump over?
EDIT: changed wording to underline that CX is much older than BMX.
EDIT2: I don't want to make you think that you need BMX bike to hop curbs. What I'm pointing to is that before BMX there was little mainstream attention to techniques like bunny hop (at least I got such impression), and after BMX got popular they spread throughout all cycling world. Though not many of us are skilled in jumping curbs, virtually everyone knows that can be done at ease by other riders.