Everything is explained to their patrons (and we all can read it too when people post here the weekly development notes) who are the only truly concerned people. This is an update that needs several new backgrounds and new characters, so it's taking more time than they initially estimated. They are 2 people (but only 1 artist) working on this game full time 7 days a week, so no matter how much money they are earning, speed is not going to increase magically. It's just how it is. If you don't believe it or you're not happy with that then don't support them but please try to be a little more patient and understanding with artistic works, especially 2D, handcrafted ones.
After all, the game is always released for free and moreover we're in a pirate forum, so I find it kind of rude coming here to say you think they are earning too much for what they are producing, or that the new update surely won't worth a 6 months wait without knowing yet how it looks, or even imply they are kind of slowering development to 'milk' their patrons. Nothing you say in that sense it's going to change anything, it can only bring hate and stress to the dev team, and I can tell they don't like this situation either, as any informed person should know that delivering updates after longer waits is usually counterproductive from a financial point of view.