The things the author does to go from 7K/year to a 100k/year looks awfully a lot like selling support or services.
Unfortunately, it's not available worldwide.
That, or using a very restrictive copy left license.
GPL would protect more user freedoms and potentially avoid big SaaS providers making profit off of your product, but it won't help you earn money just like that.
True, but depending on what you created, it might open up the path to dual licensing.