Because space in public and academic libraries is limited, collections are often "weeded"--older books are removed so there will be space for newer acquisitions. The books removed are usually those that rarely or never get checked out, have outdated information, such as tax preparation guides from the 1990's, or are in poor condition.
However, books that are old yet still useful often get swept away in weeding campaigns. The Whittier Public Library in California once had a copy of Henry Hazlitt's dystopian novel The Great Idea (New York: Appleton, 1951), but except for handful of academic libraries, this volume is only available at one public library in my area. Similarly, Bella Dodd's memoir School of Darkness (New York: Kenedy, 1954), once available in the Los Angeles County library, is also hard to find, although it's available online at http://yamaguchy.netfirms.com/7897401/dodd/dodd.html.
In Southern California, public libraries which are not aggressively weeded and where older books are often available include the Los Angeles, Pasadena, Glendale and Pomona public libraries.
I see local leftis librarians getting rid of or not replacing items of cultural significance such as important poetry books, important works of fiction and of course biographies of prominent historical folks. Part of what libraries are for, are to brouse... to find things out of one’s zone.