It does seem likely that the 78rpm record helped to set the standards for the expected length of a song although it really doesn't explain the popularity of the 10" 78 over the 12" for popular music. Obviously, there would be some advantages for the seller in materiels, shipping, etc. and there would be some for the end user who would have a lighter, easier to store product.
However, the classical music lover was happy to use the 12" in order to have fewer interruptions for record changes but even then, it was jarring for a music lover to have to hear a Brahm's Concerto break off in mid performance while the record changer whirred and clunked and another disk fell to the turntable and then awaited the descent of the tone arm which would be followed by the "schkerrrrrrr" of the empty track until the needle spiralled in to where the muscic began once again. This was not very conducive for a sublime musical experience and one classical music lover was determined to do something about it.
Years later, I had the chance to talk to him about this. As I recall, he said it was a Brahms piece that pushed him over the edge. His name was Peter Goldmark and he worked for Columbia Labs, he may even have been the president. He generally gets credit as the inventor of the LP.
Later he wanted to extend the joys of music listening into the automobile and he invented a turntable for a record player that would work in a moving automobile as it drove along highways or city streets. It was quite an achievement, reliable continuous sound before there were computer chips to read the music ahead and store it in an anti-skip cache. Unfortunately for him, his invention was overtaken by the cassete tape deck and so remains an engineering marvel that got washed up on the shores of Irrelevantania. (I've always felt comfortable there, myself. I speak their language.)