It boils down to who and why someone is distributing the software to you. A corporation expects to eventually get some profits out of its actions, so it'll sometimes do things against the best interests of the users, because they benefit itself; on the other hand you expect a community-driven distro to be made by a bunch of people who just want to use the software, and have a vision on how it's supposed to be.

Canonical suddeny made Ubuntu closed-source?

Canonical can't make Ubuntu closed-source. Most of the code in Ubuntu was not made by Canonical, but by third party developers; Canonical is just grabbing that code and gluing it together into a distro. And most of those third party devs released their code as open source, and under the condition that derivative works should be also open source (the GNU General Public License - note, I'm oversimplifying it).

What Canonical could do is to exploit some loophole of the license in the software from those third party devs; that's basically what Red Hat is trying to do. In the short term, people would likely shift to Linux Mint (itself an Ubuntu fork) or make their own forks; and in the long term, fork another Debian derivative to build their new distros from it. (Or adopt Linux Mint Debian Edition.)