It facilitates a move.
And radical downsizing apparently has some benefits for psychological well being for some people, therefore the recent "minimalism" trends.
I tend to doubt that these effects are more than short term and while I am all in favor of criticism of the excesses of consumerism I am skeptical of minimalism as a fad.
And a CD or Vinyl collection is not really comparable to having too many cheap H & M clothes or getting the newest electronic gadget ASAP. There are no classical recording sweatshops, for all I know, they don't really take up that much space etc.
The other point that has prevented me from major culling/downsizing is that it is financially hardly worth the effort. When CDs were still quite expensive, 20-25 years ago, second-hand-shops would buy full price discs around a third of new price and sell them for 50-60%. But today with a used disc typically fetching a few cents to about 3-4 $/EUR, why bother?