Most public libraries are popular reading libraries, meaning that the bulk of their budgets is set aside for materials which will be popular for the readers in their communities. They usually have reference materials, but those are generally limited to the basics so that people can just do basic research.
Most libraries have staff who are assigned to select reading materials. I don't know of any but the largest systems in the US that have people who only do collection development. I worked for our local library for ten years. It was ranked in the top ten systems nationwide for the number of people we served. We had a healthy budget, and a huge collection, and the selection committees were voluntary (except for a few of the really unpopular ones, which were assigned). There were two kinds of selections made at our system. Librarians in each library were assigned certain parts of their own collections to work on. Different areas of the county had higher or lower demand for certain types of materials, and it was up to the librarians in each area to know what the people in their areas wanted, and stock the shelves accordingly. The other types of selections were made by committees made up of people from all over the system. Those committees did things like order popular movies and music, and also best sellers, both fiction and non-fiction. They worked with monies set aside specifically for best sellers and AV materials, rather than with the budgets of individual libraries in the systems.
If your library has a really cruddy collection, I suspect it is because of one of several reasons. They may have a tiny budget to work with, so they may be trying to pick up just a few items they think will be popular with the readers in your area. If super conservative claptrap and crappy romances are what is in demand, that may be the only thing they feel they can buy. They may have a collection that is developed significantly from donations, which does happen in some very small systems. They basically catalog anything which is donated and throw it on the shelves. Those types of collections really stink, because they are entirely dependent on the goodwill of the people in the area. You end up with the dregs of other people's book collections, or basically the junk they don't want to keep. The other thing that may be happening, and this is also depressingly common in really small systems, is that there may be just one or two people doing the ordering, and they may be more interested in the things they want to read than in providing variety.
Since you are unhappy with the collection, you need to write to the person who is in charge of the library. You will need to find out if it is simply a single library, or if it is part of a larger system. If it is part of a larger system, before you complain, find out if other items are available at other locations, as those items are usually shared throughout a system. It may be as simple as having books you do want to read sent to you from other branches. If there are no other branches, you need to do a little research, and find out how much the library budget is, and where the operating funds come from. If they come from your local taxes, they they really need to stock a larger selection of titles. If they come from private donations, you may need to step up and donate, or do a fundraiser to help raise money for more books. If you are helping pay for the library, either directly, through donations, or indirectly, through taxes, they have a responsibility to make sure you are getting some benefit from the library. It may simply be a problem of not having enough resources for people to do ordering. Many small systems will allow regular patrons to join committees where people decide what books would benefit a collection. They then make the recommendations to the person or people who hold the purse strings, and the books are ordered.
For now, the simplest thing for you to do is go into the library, and ask to speak to the branch or facility manager. Tell him or her that you would like very much to use the resources, but that you find the collection very small and unappealing. Ask them who you should contact to get more variety on the shelves, and also ask if there is anything you, as a patron, can do to help that happen. I know that at a lot of small libraries, they will simply take patron requests and try to work them into the budget. If you say, "I would really like to be able to check out the books which appear on the New York Times Bestseller List", that may be all it takes.
There is one more thing of which you should be aware. There is a wonderful program called Interlibrary Loan. Basically, it's a program where libraries agree to loan items from their collections in exchange for borrowing privileges from other systems. Find out if your library belongs to that system, because it can be a wonderful thing--if you can provide them with a title, and an author (an ISBN works great, too) they can borrow the items for you from another system. When I worked at the library, I reguarly requested weird, obscure titles that interested me, and they simply borrowed them for me from outside the system. I got a lot of books from libraries in the US, but I also got books from as far away as Europe.
I wish you the best of luck. Libraries are so important, and such a great resource--it really stinks when they suck.