I'd rather not have to deal with the problems deraileur's pose when they **** you over.
It makes me look forward to riding in the wet, rain, hail and snow because there's no way more fun to get around, bicycle wise.
It's really fun to do skid stops and a zen feeling to balance the perfect, undisturbed trackstand.
The more you forget about your bike and just realize you're 'there' while riding, the better.
I like the simplicity of it, maintanence is low end.
They are aesthetically pleasing.
It's a pretty good work out, and definitely better then a single speed.
Once you start riding them seriously, you feel like the chain has just snapped everytime you go back to a freewheel and coast.
If you're lucky to have an undisturbed hill in front of you, it turns into the most fun, scariest thing ever when you simply pull up on the pedal clips because you accelerate so fast it's scary.
It's a completely different way of riding and adds a breathe of fresh air to your regular riding commute to work / school / the grocery store.
Great for cadence.
If you ride with no brakes, you become very creative in how you ride and quickly realize that you are all you have so you better learn to skid as good as a messenger.
It's fun and fulfilling.
And it's a conversation piece which is an added bonus.