When you can record in your house with minimal equipment for little money and achieve good results, why would you choose to record in a studio?
I believe the answer is perspective. The perspective of objective ears and a creative space can make the process much smoother and provide some peace of mind for the artist, giving them the headspace to focus on performing and creating to their best work.
Having had a mixing studio in my home for a few years I find, as an engineer and a musician, it is much more productive and generally nicer to go to a separate place to work. When I was mixing in my previous room I would often work stupidly long hours that were fairly unproductive, whereas now I book out Gran’s House for a day and do eight hours of good work rather than sometimes twenty of unfocussed work. I feel that this is one of the biggest pros of a studio without even taking into consideration any technical aspects of a studio.
My room at home had acoustic treatment of sorts but it was nowhere near perfect, and the consistent listening environment a good professional studio should strive for is worth every penny of investment in treatment. This became apparent to me when I moved my monitors into Grans house; I was of the mind that my budget/homemade treatment was fine and that my reasonably good speakers sounded how they did. Within a couple of projects and days of listening in the professionally treated room, I was perfectly comfortable with the way my monitors sounded and continue to be.