why cant play guitar standing up?

i can move my hands up and down the frets easy its just i cant play half as fast as i did sitting down and i mess up about twice as much why is that? like i will play the wrong strings and i cant do that thing where u strum up and down really fast did that happen to every one who tryed to stand up and play for the first time?

Sitting down your guitar is fairly securely held and will not change position easily depending on how its being held .
Standing you need a strap to hold the guitars weight and the guitar will move easily , turning around the point where the strap connects . Many players have it too high or too low for a good playing position .
It does take a bit of practice to get used to the new position .

My attempt to play Bell the Cat by LM.C on guitar