Originally Posted by fotoguy
I thinks it's mainly because of it's installation screen which tends to make people a bit nervous.
I think this is quite true.
The other thing is that Slackware does not offer to set up partitions automatically.
Partitioning can be intimidating the first time. When I did my first Slackware install (then redid it three times that first day because I didn't read the screens diligently), I found cfdisk to be much friendlier than fdisk, because it helped me to visualize the entire disk more easily than did fdisk.