Insist? While it is easy to find programmers to contribute to a community project for free, designers expect to be paid. Not everyone has enough spare cash to pay a professional designer. So they do the design themselves to the best of their ability.
I’m not talking about people who can’t afford paying and needing one, but even those can find a designer to help them if the project is interesting enough. I have done it myself and it’s been good for everyone involved. But my comment was targeted to the “I could totally afford a designer but I’m good enough myself” when most of the time is just ego speaking.
