[Platapus]

Why are there no new "decent" sailing ship video games coming out?

Simple. There is no anticipated market for such games that would justify the development costs.

Video game development is a business. No one in the major video game business is going to think "hey, there hasn't been a xxx game out in a long time, let's do one!".

One would have to do a market study and determine that there is a sufficient probability that a minimum number of people will buy (not pirate) the software in order to not only cover the development and distribution costs but also make a profit.

While there will be a limited number of people interested in such a game, and I include myself in that group, I doubt there is enough interest to justify the costs.