JU_88 does have a point.
In this list, how many sub sims do you see, and how many are recent games?
http://www.subsim.com/subsim_reviews_index.html
Now, what were the 3 (edit 4) most recent sub games?
# Silent Hunter I, realeased in 1996
# Silent Hunter II, sequel released in 2001.
# Silent Hunter III, sequel released in 2005.
# Silent Hunter 4, released in March 2007
Nobody else is making them. Probably because nobody else wants to, because theres more money to be made in other game genre's. Money is ultimatly the bottom line, its why companies exist.