It's pretty simple to understand why fishing games fail... They aren't done well.

This is a fast explanation how to do a fishing game properly.

First thing,

) Aquire the rights to Pro Fishing Challenge. It's the best all around fishing game ever made. Or don't, but at least see how they did it.

) Upgrade the graphics- The graphics are important but they can be subpar, just not as subpar as they are.

) Add more and different types of fish. There's a glitch fish that has never been caught, I'd like to catch it.

) Add mini-games such as boat races and casting contests.

) Add a crafting system (Ask me about it)

) Breeding and Tagging- how cool would it be to breed my own fish... Very cool. And how cool would it be to tag it and release it so other players could catch it and get rewarded for doing so? Friggin' awesome is what it is.

) Add salt water fishing in addition to freshwater fishing, Y'know, with the big boats and big ass fish... I mean exciting monsters of the deep..

) Maybe add some RPG elements

) Housing

I don't think fishing games could ever be overdone, but they are always underdone.

That's it for a quicky.