My understanding of it is that as a beginner, it doesn't take much work to stimulate progress, be it in terms of strength, size, or some other measure. You pretty much just have to look at a barbell and bam! There's 10lb of new lean body mass. Since progress is stimulated with relatively little work, a high amount of volume isn't needed, thus recovery needs are low and you can do everything more often. As you progress further, it takes more than just showing up and going through the motions to spur on new developments. The volume required by a lot of intermediate and advanced lifters to make even a little bit of progress is often so great that it takes longer to recover from.