Why did some music producers in the 1960s not want double-sided hits?

In my teens, I had a 45 of “Wipe Out” pressed in the 1970s that had “Surfer Joe” on the flip with just three verses. I gained some appreciation for it when I discovered the original with all five verses. It’s got a really nice story arc in the longer version, loading up his woodie with 26 boards, sneaking off base to surf Trestles, doing KP as the result…