They Bought? Or donated by fools who thought they were going to keep and display the items for all time. Most museums will not spend a dime for anything or at best have a sugardaddy buy it for a tripple tax writeoff.

At least they’re auctioning the loot off publicly. So called “curators” have a strong tendency to sell things out the back door to their friends and family. 

Having spent 15 years in Museum administration.  I will not comment on this specific situation since I don't have any factual background on it. 
but I could go on and on about the evolution and development of museum professional and legal practices.  Suffice it to say that there ARE professional standard practices to safeguard collections.  Many museums have implemented those practices and guidelines and have achieved certification by organizations like the American Association of State and Local History and the American Museums Association. Such accreditation requires firm clear and aboveboard legal policies and practices for both acquiring and disposing of collections, including a museum's dissolution.
However there are many small local and community museums founded by well meaning folk who simply cannot afford to operate professionally and many abuses do occur. 
One of the major problem with them is that artifacts, some of great significance and value were put on "long-term loan" in generation's past at eh museum's foundation with little or no documentation of current ownership. 
  As community budgets collapse in the current economy attempts at political economics overrides professional standards.

Another problem area is the private museums owned and financed by a well heeled backer or family who hire "experts" to locate and acquire artifacts to flesh out and augment a family collection to create a "museum" as a celebration of the family. 
Often these are little more than bounty-hunter scroungers who practice all sorts of chicanery for their own benefit.  In some known cases, once found out the museum's owners decline to prosecute rather than expose their pet museum to embarrassing publicity

FWIW:    Just heard this AM on the news that the City of Detroit is "considering" auctioning off the collections of the Detroit Institute of Arts and the one of the large art auction houses is being approached to "evaluate" the collection.    If this is real, and not just a political ploy;  (like high schools threatening to cut off athletic programs)  it is going to create a nuclear firestorm in the museum and arts community.   It is not as well known and certainly with the "condition" of the city not as well visited as it used to be, but it is certainly one of the top 10, maybe top 5 fine arts collections in the US. Certainly on a par--or it was a decade ago, with the Chicago Institute of Arts.
 Just the legal fighting such a step will entail will last for decades.   Legally putting a properly constituted museum out of its misery is an expensive and very complex step that will consume a large chunk of the proceeds of the sales. As I said, I know nothing about the Penn. museum; but the DIA is certainly among the forefront of properly and professionally organized and operated museums.  In my museum training it was one of the examples used for how things should be organized

Sell the DIA?  OMG, that would drive the fine arts market downward so fast and so far your head will spin.  There simply aren't enough cyberlords in the world to pay full market price for the treasures in that place.  Yeah, by the time the legal wrangling was finished, Detroit would have been essentially abandoned . . . along with the rest of the planet.  Tachyon drive, here we come!

And that 2.5 Bill is only on some 38 artworks.  Heaven alone knows what the total value might be.  Depress the global art market?  I would guess so!