When an application becomes default in Ubuntu, does Canonical pay the developer(s) for making it default or do they just use the application for free?
All of the default applications in Ubuntu are free software, and in most cases, certainly in all cases that ship on the CD, that means they are not for sale.
If Canonical did pay, it would be a gift. They ship software under the same licenses the software itself ships with. So, in most cases
- there just isn't any product or service that Canonical could pay for, even if they wanted.
However, Canonical and other Linux distributors do sponsor by employing developers to work on software, of course. And, like TheX says, they contribute to the software itself. Which is the whole point.
They "pay" by contributing any bug fixes, feature upgrades back to the developer, as consistent with the nature of open source software, not to mention the press that such applications get by being included as the default software of a major OS.
Open source software is determined by the license. There is nothing to stop a company from paying a software developer and then licensing their work as GPL for example. Clearly most open source developers aren't paid for their open source work.
Canonical isn't Ubuntu; it's a multinational corporation that finances, owns, and controls Ubuntu. Canonical sells support, and software services. But, they have hundreds of millions in revenue, with offices around the globe. While it's true, the software in Ubuntu is largely not created by Canonical, it's not true to state that "Canonical does not pay developers".
For example, Canonical paid
- Scott James Remnant to create Upstart
- Alan Griffiths, Kevin DuBois, were either on contract or paid for the development on Mir.
- Mathieu Trudel-Lapierre on Network Manager
- Michael Hudson-Doyle developing Launchpad and Go.
- Iain Lane cPython/Launchpad
I would guess there is a hundred? Other projects have been sponsored (GNU Bazaar), and other open source products like Quickly, juju, Storm, and Snap.
Also in 2017, 1% of the Linux Kernel Contribution comes from Canonical (that's not a high number at all, but it's non-zero).