Slackware was the first distribution I really used, because I wanted to understand Linux. At first it was a struggle and I used Mandrake instead. Many years later I had more time to tinker with various distros, and suddenly Slackware felt familiar and simple.
I'm also a deadhead, and the church of the subgenius is great; Slackware has street cred.
The package manager is the best, I like that it doesn't have a goofy name and tracks everything on the system. I like how straightforward it is to make packages for Slackware.
I like the DIY nature. It's challenging when something breaks in Linux, but I often learn about how the system runs. I can understand just needing things to work, but it does once it's set up.
Some stuff is folklore, or general Linux knowledge. RTFM or look on a forum. Just gotta poke around.
There are a lot of things to like about Slackware. It's solid as a rock, it doesn't get in your way, it's predictable, KISS...