“Artists, collectors, and foundations donated the vast majority of the art represented in this survey. In addition to the potential tax write-off, benefactors often view large museums as the only places that can guarantee important works of art will be properly conserved. They may also seek out institutions that have a policy of never selling the work, as the Rothko Foundation did with the NGA.”

Read the full article at Quartz.

https://qz.com/583354/why-is-so-much-of-the-worlds-great-art-in-storage/