For me it's comfort to start with. No binding and pinching. The breeze is wonderful.
I have heritage on my side if I need a convenient excuse, but that's not the main factor.
Next comes style. They simply look fantastic. The kilt has motivated me to take off a bit of weight.
I walk with more confidence. Maybe that's a self defence mechanism, but it works.
Lastly, I do like a little bit of attention (Must be the child in me). The kilt is a great conversation starter!

Cheers