"Museums are icebergs of antiquity, with the vast majority of their collections unseen. In the case of the British Museum’s 8m objects, only around 1% are usually on display."
https://www.economist.com/britain/2023/08/21/stealing-from-museums-is-easier-than-you-might-think
"Some of the most famous exhibits acquired their fame less from artistic merit than because they were nicked. The Mona Lisa, until it was stolen in 1911, was little known except to art enthusiasts; it took 26 hours for the Louvre to notice it had gone. [...] The Parthenon sculptures became “this great icon of Western art because they were removed”."
https://www.economist.com/britain/2023/08/21/stealing-from-museums-is-easier-than-you-might-think