Minor changes to the satellite position? Vibration from some hardware? I dunno but the parent asks a question I ask too.

When you do long exposure, any kind of movement, even very small, can degrade your image.

How JWST handles movement during long exposure is a good question. Same with hubble.

long exposure images aren't actually 1 continuous exposure. you take a ton of individual images and composite them using known reference points.

Well I mean the JWST is in orbit both around the L2 point and the sun. It's sensitive equipment must also be facing away from the sun. So there's a lot of movement going on out there.

everything everywhere all at once