Life
Because they are rather pressing to be around. 😃
For the same reasons adults do it. To see what the limits are.
Because it's funny
It's in their job description.
Because they're immature and need something better to do with their lives.
Kids want attention, what better way to get attention than to push some ones buttons? It gets a reaction and makes the kids feel like they are important.
Kids are refreshing because they are not ashamed to ask 100% for everything they want.
We adults are used to deferring wants for various reasons.
So we both admire and somewhat resent such requests when they represent more than what we are willing to grant at the time, no matter how reasonaboe such requests are.
At least, that's how I look at my "buttons."