Roger, as already stated coz they were 33rpm, you could easily fit 2 x 1960's length tracks on one side of a 7" disc.
In lots of South American countries (Brazil being the main one), just about all 7" records were 33 rpm. Coz of that a 60's US 45 track when released in Brazil on 7" only used a tiny section of the vinyl with the run-out section takin up well over 50% of the grooved area.
So, in Brazil, they tended to put out loads more EP's, thuss the vinyl area was used more effectively.
Coz of that, there are loads of 60's & 70's LP tracks that only appear on 7" releases in Brazil.