I'm just about close to pulling the pin on one of my websites. Reasons in point form are:
Out of all my websites, it makes the least money, yet takes the most effort to maintain.
I regularly get emails from people not happy, even angry, with the content. Again, not worth it if I'm not making all that much money from it anyway.
Traffic is steadily dropping with time due to various factors which I'm guessing includes bigger and better resourced competitors as well as Google algorithmic updates which deem the site to be low quality for whatever reason.
It's a shame though after all the time I've put into it. But at some stage, I'm going to have to admit that I've been (and still am) beating a dead horse which is just going to get deader with more beating.
I'd like this thread to be for other webmasters who'd like to share their own experiences in making the big decision to shut down their site and move on.