Plugin development has a cost. Those who create free plugins either do it as a hobby, or their employer sees it as a way to bring attention to their company, so they can sell a related product. At the end of the day, quality plugin development can only be achieved through a lot of time and effort, and that requires ongoing revenue. There is no such thing as free.

Auttomatic has services, but they also have a captive audience to promote those services too, so their business model won't work for everyone.

Selling plugins and themes under GPL, rather than offering the same software for free, allows the developer to continue development, along with support, and updates, which can include bug fixes, security fixes, and compatibility fixes. Anyone who has downloaded a plugin from WordPress.org knows it is rare to find a good quality FREE plugin, even from the largest WordPress repository in the world. A good trusted developer you buy a plugin from can provide a reliable product, because that developer needs you to pay the bills. That is how business has always worked, since there was such as thing as a business.

One of the biggest difficulties for developers though is how to provide plugin and theme updates, so like Brent, I developer an API Manager for WooCommerce to allow developers to sell their own products, and provide automatic updates. I would not be developing this software if it wasn't being financially supported, because it requires so many development hours. The best plugins cannot be developed for free.