The cause may seem self evident, but by in large I disagree with your premise.
The appeal to this insomniac is a place to let your mind race in the hopes that it will idle down.
Oddly enough I'll also assert some of the crappiest diners also have some of the best coffee, burnt to perfection at times, genuinely quality stuff much less frequently but it does happen.
It's not the coffee keeping me up, it's everything else I was thinking about before I even considered the destination.
Meeting people and discussing ideas is not only good intra personal practice, on occasion you even meet that perfect stranger that just changes your perception of reality.
scratch that, more frequently than not.
Weather for the good, bad or indifferent at the very least it's a good place to people watch and self evaluate.
On occasion it's actually relieved my insomnia, either by way of burning out my neurons by way of over stimulation (coffee and or conversation), or by allowing me to self actualize whatever the hell is bothering me.
But don't take my word for it, give it a go yourself next time you run into a bout.
It's either that or smack as far as I'm concerned...
just kidding...
maybe...
I suppose you could do that who clinical evaluation, "therapy", head drugs, blah, blah, etc.
but if you didn't know I'm not the biggest fan.
It has it's place for those with genuine physiological problems, but for the mass majority of us I think it's our own actions, reactions, attitudes and the like that may even cause some of those physiological issues.
If it hasn't got to that point ...
it is in fact all in your head.
Think about it.