Why do we build alone?

I thought of an idea. I am curious about other people's experiences and thoughts on this subject.

Since most people are not experts in every field, whatever part of the project they do, they waste a lot of time in other parts and it does not turn out the way they want. The backend guy has problems with the frontend, and the technical guy with marketing also has problems. And mental difficulties because you are trying to do something you do not understand. What if we launch small projects serially with a group consisting of 1 frontend, 1 backend developer and 1 marketer? It's like startup studio but indie. At the same time, we don't expect people to give their whole week. These projects become side projects for everyone. If I created a group like this, would people join or would they want the whole cake for themselves?