Because people gauge their success on forums by the number of threads they create and how long those threads are.
List threads are easy to post to and when you don't actually have anything to talk about "what's your favorite..." is an easy way to boost your count.
They are also very easy to repeatedly post to: "I like A & B" "Oh, I forgot to mention C it's awesome" "yeah D is good too, I've seen it" "you like E too?" "I haven't seen F yet, maybe4 I'll check it out"
inane and pointless threads that are not allowed here.
List threads are easy to post to and when you don't actually have anything to talk about "what's your favorite..." is an easy way to boost your count.
They are also very easy to repeatedly post to: "I like A & B" "Oh, I forgot to mention C it's awesome" "yeah D is good too, I've seen it" "you like E too?" "I haven't seen F yet, maybe4 I'll check it out"
inane and pointless threads that are not allowed here.