There are many reasons to have no copies of a book, with the simplest being that nobody has requested it yet. Framing that as “banning” is ridiculous, since it falsely implies a doctrinal intent where only ignorance or concern for stated demands exists.
What you said is not curation, it's just managing the stock. Having 57 copies or 56 copies does not substantially alter availavbility. If somebody removed all copies of Atkins books, because "nobody needs them anymore" - then yes, this would be a doctrinal decision. Admittedly, since diets (for some reason) aren't part of culture wars (yet?), not a very controversial or scandalous one, but if some Atkins die-hards occupied a political position, or, in the contrary, Atkins were declared racist for some reason, it could become one.
> There are many reasons to have no copies of a book, with the simplest being that nobody has requested it yet
But how I can "request" a book that isn't in the library? Most libraries I've used do not have this function, not at least any that I could locate as a regular patron. On the contrary, I am reasonably sure most of the books featured on my local library's home page, aren't there because some patron came to them and asked for this specific book, which previously wasn't part of the collection and wouldn't be unless specifically requested (in fact, again, I know no way of doing this). Looking at their published collection developing policy I see (among others):
Provide a diverse and inclusive collection that contains content by and about a wide array of people and cultures
Consider the appropriateness to scope of the collection as it is developed
Content created by and representative of marginalized and underrepresented groups
Attention of critics, reviewers, awards and public
Suitability for intended audience
Literary or stylistic quality
Tell me these are non-doctrinal criteria. Of course they are - one's high quality suitable inclusive book is another's offensive bigoted trash. Again, it's about who has the power to make such decisions. Of course, the librarians, seeing themselves as The Experts (TM) would claim exclusive right to make such decisions on behalf of people paying for their library. But are they entitled to that, absent any control and supervision?