On classic vinyl releases you got a single record with roughly 20 minutes of music on each side. They recorded the album so it fit nicely on two sides.
With new releases the vinyl is usually an afterthought, so it usually doesn't fit nicely on two sides, so they just throw an extra disc in the sleeve and spread the songs evenly and you end up with 3 or 4 sides with 12-15 min music on them.