We should all appreciate that most homes were not done by teams of professionals back in the day. Multiple things can be true here, 1) building your own home will take a lot of time to get right (so time being used in place of money), 2) the skills involved are all completely learnable and do-able for an able-bodied person who again is willing to put the time in, and 3) its not worth it for the vast majority of people who don't want to learn these skills and would rather focus on their own work and pay someone else to be a professional in the space. And yes 4) I've seen quite a bit of DIY work in homes and sometimes its impressive but usually its questionable and sometimes even horrific.