@chatnoirchatgris
QI's pretty great, although you do have to remember that it's primarily entertainment in addition to educational. You may have also watched a segment where Stephen Fry talked about the "half-life of facts," as what is considered a fact
now may not necessarily remain a fact 5 or 10 years from now as its foundation is revised to new information.
Case in point, giraffes - as far as I remember - are said to branch off from the same family as the okapi, a short-necked mammal that's typically called the zebra or forest giraffe. And as far as I can tell, no-one has yet to find fossil record of transitional species that precedes the modern giraffe. So we don't know whether it was a spontaneous mutation, or a gradual one. There
might be evidence to suggest it started branching off during a period of droughts, where severe competition would be disastrous.
If anything, that they have some inconveniences from their long neck is just further evidence that evolution is a messy process that's more likely to get things wrong in the process of being right. Case in point, when our distant ancestors stopped being a tree-climbing species, our lower hands gradually became feet.
But, we can trace all of our common foot problems to this very process, because evolution stopped working on our feet the moment it felt it was "good enough." Functionally, our feet still to this day has components that you're likely to find in hands, like the ability to flex forward to an extent (which is completely un-needed, and leads to some of the worst cramps ever) and a few other bits and bobs that are functionally useless, but more moving parts for things to go wrong.
That said, I have no intention of changing your mind. As long as they're merely hypotheses, it doesn't matter what we think or feel is more correct until more/new information comes in that definitively makes it clear one way or another which is right. I think it's because of food, because that's important for survival. But I can definitely see the argument why it'd be for procreation, since that too is important for the survival of the species as a whole.
I still think the head-above-water hypothesis is charming/funny, though. I will literally bust my gut laughing if that ever becomes the official theory.