A GPT you build for yourself saves you time. A GPT you build for other people becomes a product, a service, or a paycheck that arrives every month. Same skill, aimed outward instead of inward. The person across the table has the same problem you solved for yourself, and they’ll happily pay you to hand them the answer.
Here’s what most people miss. The skill of building a useful custom GPT is rare enough right now that people will pay just to skip the learning curve. A coach doesn’t want to learn prompt setup.