I do not really know why so many stores keep selling tobacco. For stores like Costco/Sam's who do full case sales and have a lot of resale customers, I get it..
Every store I've ever worked in, tobacco was a problem category and we always were hearing it lost money. If it wasn't due to theft, it was due to inventory errors, or due to spoilage/improper rotation. Tobacco customers seem impatient and having a case that someone has to "walk to" and "unlock" seems to annoy customers. As far as I'm concerned customers should just buy tobacco at gas stations that seem better equipped to sell the product and usually have better prices too.
There is also a chain called Dotty's who runs slot parlors (which allow smoking inside) who also sells cigarettes at very low prices. Dotty's took the slot traffic from many grocery store slot machine departments (which used to allow smoking inside but no longer do) and I think also has taken a lot of cigarette traffic from grocery stores.
Nevada is a pretty big tobacco state due to the casinos and that smoking is a big part of casinos. Yet outside of the casino environment I really do not notice all that many people who smoke anymore.