[jrochkind1]

Were they literally from the Smithsonian?

Either way, libraries/librarians deaccession books all the time that outsiders might think "that's so valuable, why'd you get rid of it?"

There is only so much budget/space to store stuff. You get rid of stuff that is no longer relevant to your mission, or lots of other libraries have so you don't need one too, or just isn't _as_ important to your users/mission as other stuff. No library has infinite space.

[cestith]

You also reclaim space if you have multiple copies of a work and the demand for the title in your collection is limited. So even if you've received a copy that was formerly from some library they may have kept a copy or two if they used to have a dozen in circulation.