I've certainly wondered why they weren't interested in being more transparent.

The development is pretty transparent, if you know where to look. The ChangeLog.txt is the main place where development updates happen (especially the -current ChangeLog, but security updates for stable happen in the respective release's ChangeLog). There's also the mailing lists, and the key people in Slackware hang out on the linuxquestions forums and ##slackware (freenode).