Why are people so worried about the gender?

Why is it so important? What if they say it's one gender and it turns out it's another. So? I swear it wouldn't bother me a bit :) so I obviously don't understand anxiety. And when I see how people are nervous about the gender I feel the need to tell them - it really is not important :) you have a healthy baby, why would you be nervous let alone dissapointed... And in this app I saw people beyond dissapointed, and I just DON'T UNDERSTAND? :)