The reason a lot of people go through the trouble of breeding the perfect shiny, or capturing a shiny is for one simple reason: to show off! Especially to your friends, haha. As Furious said, it's really ego-boosting when you hear your friends go on about your shiny. It's a great feeling. :)
I personally feel that if you're constantly failing at breeding a shiny Pokémon, the trial and error you went through in order to hatch that shiny is especially rewarding. Sure, hatching a shiny on your first try is nice and all, but personally, I don't feel that sense of accomplishment, and it becomes less rewarding.
The same goes for catching shinies. Encountering one on the get-go is really amazing, but I feel like I didn't really earn it. As opposed to trying over and over and then finally finding one. It's a great feeling and gives you a sense of pride. You worked for that shiny. It wasn't just handed to you.
Whether you keep hatching or catching shinies one after the other, the sense of accomplishment you had originally just fades away, and getting one just isn't as rewarding. I think so, at least. :P