>There are gains to be had from exhibiting private artwork in an internationally renowned institution; inclusion within a curated major exhibition lends it credibility and legitimacy, which can be added to an impressive provenance trail, making it attractive when put up for sale.

We gain putting things that are "hidden gems" and telling people it's good, for prestige, and/or leading up to sales. Art collectors that care about money aren't usually art appreciators. It's just a slow version of bored apes.