What Makes Horses Addictive?

I think about this all the time, so wanted to write about it, but every sentence, phrase and word I attempt to write sounds like a tired cliche. The questions, about myself and others, come easily:

1. What drives us to take on a responsibility that requires us to go into -15 or colder weather, several times a day, sometimes for weeks on end, to feed horses, make warm mashes, and clean stalls, even when we can't ride because of the cold?
2. Why would a sane person, when so fortunate as to retire at 50 (potentially enjoying many years of riding), risk it all and work like a dog to be able to have even more horses and more horse activities?
3. Why do young mothers (and fathers) go to the barn night after night -  taking lessons, training horses, spending money that's needed for many other things, tired out after a long day's work, and with many other activities clamouring for their attention?
4. Why do we (often daily) work to the point of shaking with exhaustion and tie up ALL of our money, for those elusive moments in the saddle when it all clicks?
5. Why do we keep riding when we go through periods of such fear that even thinking about riding makes us throw up?
6. Why does a physician ride a gorgeous 17 hand five year old, when her doctor has told her if she falls he won't be able to put her back together?
7. Why, instead of a relaxing vacation, do we pack up trailers and go to (what can be) the stressful world of a horse show? 
8. Why do we get back on our horse 3 days after breaking ribs in a fall, barely able to catch a breath because of the pain, when our doctor has told us to wait 4 to 6 weeks?
9. Why are we smiling as we shovel shit?

It does seem to me that there are similarities to addictions, as we sacrifice so much for our fleeting fix, but I have no idea how this works.
I don't have any answers to the questions I pose, I just have an awareness of a happiness that would be emptiness without the horses. These phrases come to mind when I think about what horses give me:

• A soaring, transcending joy
• A deeply, all encompassing, loving peacefulness 
• A communion with another species that I experience as spiritual

I told you it would sound like tired cliches. I'll keep trying...