From an update posted to the Slackware news feed yesterday:

“This shouldn’t really be a surprise on any level. The poll on LQ showed a large majority of our users were in favor of the change. It’s my belief that the MariaDB Foundation will do a better job with the code, be more responsive to security concerns, and be more willing to work with the open source community. And while I don’t think there is currently any issue with MySQL’s licensing of the community edition for commercial uses, several threads on LQ showed that there is confusion about this, whereas with MariaDB the freedom to use the software is quite clear.”

(Here’s a link to the mentioned poll)