I completely get why this policy makes sense. However, a part of me finds it a bit sad that there may be rarer old gems in the library that aren't so commonly found in bookshops anymore, just waiting to be discovered and enjoyed, which could then be chucked out and replaced with a whole load of recent stuff that most people are already familiar with.
I wonder if any efforts are taken to promote the books that aren't borrowed at all; i.e. are people seeing them and deciding that they don't interest them, or are they just not seeing them at all in the first place?
I guess my thinking is that libraries shouldn't just be for the most 'bums on seats' books - although obviously, shelf space is at a premium. Just as BBC4 will show many programmes that only a minority of people will ever want to watch, I think there's a place for preserving non-popular, but (to the right audience) very fascinating and informative content. If BBC4 started showing Mrs Brown's Boys instead of its usual scheduling, it would get a much, much larger viewership; but that simply isn't what it's there for.
Is it the Bodleian Library - and maybe another(s) - that automatically receives a copy of every single book that is published in the UK (presumably at least by recognised publishers, if not all the self-published ones)? The vast majority of those books will have a vanishingly small audience, but I still think a library is very much where they belong. I know we have the internet now, but I don't see the sole purpose of libraries as needing to only cater to the populist titles, without there being a place to house and 'protect' the worthy but low-interest titles.