There's at least two issues with this line of thinking:

1. many astronomical observations are long integrations (many minutes of open shutter) and you often cannot read out the pixels during the exposure. So you can't selectively ignore pixels on a "by moment" basis. And with enough satellites, enough pixels could be affected to render an entire image effectively unusable

2. It seems you're thinking only about optical astronomy. There's also a ton of radio/millimeter wave astronomy that's done from the ground. Satellites have radio-wave downlinks that can be powerful enough to destroy the electronics used in radio astronomy receivers. The US's National Radio Astronomy Observatory has been working on data sharing with Starlink to mitigate this, but it's basically up to companies to agree to work together. Other satellites / companies don't engage in this coordination and so some radio telescopes need to go to a "safe"/stow position to protect the electronics. This costs valuable observing time.