There are technical reasons why 45rpm discs could sound better than 33/⅓s, but one reason for the proliferation of 45rpms is that the number of craftsmen who know how to cut long playing sides has greatly diminished due to retirement and death. For the same length of music it is easier to cut a 45 than an equivalent 33⅓ at the same level of fidelity.
Who asked for this?
I personally think the new 2-album 45 rpm craze is a PITA and that the record companies could have brought out a product that was 98% as good on one 33.3 rpm disc. Who wants to clean and store and extra disc with every record? Well, the vinyl industry must have heard my plea and is now releasing an even bigger abomination: FOUR single-sided 45 rpm discs per record. I'm sure you can't wait to get your hands on this stuff so you can spend even more time screwing around with the records and less time listening. (nothing personal - just a rant)
http://store.acousticsounds.com/d/61219/Dave_Brubeck_Quartet-Time_Out-45_RPM_Vinyl_LP
http://store.acousticsounds.com/d/61219/Dave_Brubeck_Quartet-Time_Out-45_RPM_Vinyl_LP