For me it's largely to avoid the temptation of things like being able to immediately review the photos and "I can take another". I'm very much someone who wants a quick uncritical snap of a moment and very little interest in how well it's framed or how the people are looking though.

Also a bit sick of having thousands of photos that I'll never get around to curating into anything worth my time looking back on. They all just get dumped on an external hard drive and never looked back on.

RE: the cost it can be cheap enough. B&W is very easy to develop at home for not much and if you get a half frame camera you can get 72 shots from a single roll which can take an incredibly long amount of time to get through.