Why desktop? Because images are meant to be viewed.. And because GPL FLIF won't become a standard for web browsers, a desktop app would be the most logical way to view these images (unless you want to convert it to PNG, which defeats the purpose of having a new standard.)
The lack of desktop apps that use GPL that are profitable is the glaring proof that GPL is not good for developers in that rather large market segment. Web-based services use a lot of GPL, but they have a free pass from having to release all their source code that touches GPL code.
I'll add that I am a software developer. I write desktop apps, web services, and pure server apps that I sell. My apps sell online whether I'm on vacation or working for a client, learning new code, or adding features. By avoiding GPL, I can use my software anywhere I like, sell it any way I like, and not worry about hiring a legal team to review compliance with the licenses. More importantly, I don't have to perform tech support to get paid for my own work-- that would limit my ability to earn money to the number of hours in the day I want to work.
I prefer two ideals: "write once, sell many" and "willing seller, willing buyer", as it works well for me. Unless you're retired, or happy to live as a pauper, how is "Sell your software, but give it away if anyone wants it for free." a better strategy to earn a living? I'm sure I just wasted a lot of my and your time.. but who knows.