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I think it had more to do with the fact that relatively speaking, the LP was still kind of the new kid on the block. The concept of the single was as old as the first commercially recorded music. Singles were on the radio and what people cared more about. Also the artists weren't trying that hard to make cohesive albums and were promoting singles way more than albums. The real age of album oriented rock only began kicking in with the later 60's and the rise of FM rock radio.
David Kitching said:
The reason singles were so important in the sixties was that LP's were so expensive. Another reason was the already mentioed filler tracks, I'd hear people saying how they'd bought an LP and there was a load of boring crap on it. And they wouldn't buy anything else by them.