Wanda Jackson is still performing and making CD’s. She is now 75 and made a recording with Jack White in 2009 and has another coming out some time this year. If you have never seen her check her out on yuotube. It wil be a revelation.
Instrumental rock - so called “surf music” - was huge from the late 50s to the mid 60s.
So, between the rock’n’roll era and the Beat music boom, we had Motown, Phil Spector/Brill Blg/Girl groups, the folk revival (which actually began in the early 50s) and instrumental rock. Also doo-wop, yet another style that was huge for a few years back then.
There was just so much going on at the time, musically, that rockabilly just got lost in the mix of styles.
Surf music was a tiny and obscure corner of the market in the late 50s/early 60s. There were the Ventures, who may or may not have been considered surf by the purists, a few others who broke out and had national hits, a few who had regional hits, and many who weren’t rediscovered until after Pulp Fiction.
I agree there were a huge number of instrumentals; it’s just that they were in every style, from smooth pop to rockabilly to novelty.