Same reasons for me to like being tickledI LOVE to laugh! Can never get enough laughing, plus I love the helpless state it puts me in. ^_^
The short answer is because it's the funnest hottest thing ever.
The long answer is because of the sensation, the anticipation, the humiliation, the power exchange, the verbal teasing, the loss of control....and so on and so forth Amen.
Driving someone nuts by doing what they love/hate. And I love the control I have over them!