SFMoMA is selling a 1960 Rothko painting at Sotheby's in May. It's expected to sell for $35-50 million.
Now, you may think this significant work by this significant artist, having fallen under the aegis of a museum, is held in the public trust, to be accessible to present and future generations. But clearly: not the case.
And you may think potential future donors to the museum, upon hearing this news, might ask themselves "Why should I give this to you? What guarantee do I have that you're not going to sell this tomorrow?" But again: nope.
How hard would it be for people to just admit that all the "public trust" talk is a bunch of bullshit and replace it with a rule that says museums are permitted to sell work if but only if they have a good reason for doing so? (In this case, the good reason proffered is to diversify its holdings, to "address art historical gaps like works by women and people of color.")