Recently I've been getting a fair amount of traffic on the site which has pushed the costs of hosting up, in particular the live trains layer which shows all the trains in near real time on the map at once, animated along the lines; is quite high bandwidth. The site has delivered about 3.23 TB over 13.75 million requests this year.
I decided a long time ago that selling advertising is a rather poor business model, particularly from a user experience perspective. Also from a motivational perspective. I feel like advertising and profit are poor motivators, so I'm trying to find the map by selling (hopefully interesting) prints and merchandise, as well as donations while I'm still getting started.
The longer term plan is to add user accounts with some more interesting paid features but as of the moment this is what I've chosen to do to avoid selling advertising.