Why?

I have just put the kids to bed, and I'm wondering "Why?". "Why" do they HAVE to argue? Most of it is pointless arguing, like when Jayden is watching a show and yells "YEAH!" when Buzz Lightyear defeats Zurg, yet again, and Karah screams from the other room "NO!", and they proceed to battle for the next 15 minutes over NOTHING! "YES!", "NO!", "YEEEEES!", "NOOOOOOOOOOOO!!" over and over again. Separating them does nothing, seeing as they are already in different rooms, and the only way I could get them to stop was to offer them each a cookie. Also, "Why" do they wait until Daddy gets home to behave, and when he has to leave again to work late "Why" do they feel the need to stop? "Why" do they ask me "Why" all the time? (Yes, both of them are starting that. Jay, because he's curious, and Karah, because she's a parrot.) I love my kids, and I love being a mom, I'm just wondering "Why" no one said (in a way I'd understand) it could be so darn frustrating at times!