I understand that, and that's the most common approach. If you had worked for Popcap or ArcadeLab, you would have find out, there is companies that works a lot different. The task to implement a new and original game design (or just to make a really good derivate) that is both fun and working good with the casual audience (to get a high conversion) is a tremendous pile of work. I think you would be amazed what kind of time some companies spend to improve the gameplay and make their own twists, to make it a derivate instead of a reskin. It's about years, rather then months of development time, week in and week out to add features and try them with their QA and beta testers to figure out what features will work in reality etc. Every little detail you add must be tested so it doesn't break the game, or make it less entertaining. It needs patience, experience and maybe even a bit of talent. But most of all, it needs time... lots of time.