"Shipping"

Vague Spoiler Alert:
Being about 10 years behind the rest of the world, I have recently been watching The O.C. for the first time. I am about half way through season 3 and the whole Ryan/Marissa thing is really starting to annoy me. Usually I am so invested in a series that I start rooting for couples from the start, sometimes I'm right, sometimes I'm wrong, but at least I'm invested in the characters. When it started, yeah I was hoping Marissa would dump the rich kid and get with the cute, but brooding, guy from the wrong side of the tracks, who wasn't? But as time goes on I'm more and more uninterested in the relationship. I didn't really care when they broke up and she turned lesbian, I didn't really care when Johnny turned up and "threatened" the pairing and now he is dead and Ryan and Marissa still aren't happy, shocker. To be honest, now I kind of hope he gets with this other chick who has just turned up, (Johnny's cousin I think) and I don't really care what happens to Marissa.
So this whole O.C. thing got me thinking about shipping, where people want two people or characters to get together and in most cases make fan fiction about it. It seems lately that I'm always shipping the wrong characters, which makes me a bit angry when I watch the tele. I want Elena to get with Damon, so the end of series 3 really annoyed me. I wanted Zoe Hart to get with Wade not the Lawyer man, another annoying ending and I always wanted Zuko to end up with Katara, not the emo chick. So now I'm wondering if the writers do it on purpose? Of course they do, they specifically introduce characters and plots to make people keep watching right? So if that is the case, why am I so uninterested in what should be the main "ship" of the series? Everyone knows Ryan and Marissa should be together and the point of watching is to see them live happily ever after, but I just don't care. I was happy when Stefan left and Damon could make his move and I never once complained that Lemon was sleeping with the Mayor and it was unfair to George. Is this just the product of bad writing or is that actually good writing, getting people to support both relationships so that they can chose who wins at a later date? 
What is the point of shipping? Why do we bother to root for characters only to be disappointed? I guess that is why people create their own versions of these stories so they can watch their favourite couples finally get together and bring themselves some piece of mind.
I haven't finished The O.C. yet, so no spoilers please, even if I did just ruin The Vampire Diaries for you. I did warn you.