A solution can be to outsource : hire contractors to make all that is not your core project (ex design, content...).
Yes, as a dev you can do everything, but not with limited ressources (your time and money are precious!)
When results are desired and there are deadlines, i cant afford wasting of time with trail-and-error approach for example with gui design. Even its interesting area.
This is also called opportunity cost. Famous footbal player will not cut his lawn even he knows how to do it (besides he dont wanna do it). He focus on more important things. And this important things helps him earn more money and outsource other things. And (sadly) money is root of everything.
After few years i have found out that dealing with issues during side projects increase my value in my proffesional life. I have experiences what can go wrong, where can be possible bottlenecks, which issues are just warnings (almost nobody is interested in) and which one are errors and have impact to business. This helps me a lot to take better jobs and contracts.
I was talking mainly about projects with commercial intentions.