Because the spacecraft has bright interior lights. Hop into your car at night, turn all the interior lights on, then tell me how well you can see the stars without rolling the windows down.

Same thing for why stars don’t appear in the background of photos from the moon. The brightness of the light reflected by lunar rocks/soil washes out the starlight, which is too dim to creat enough contrast. That and the cameras they brought weren’t telescopes, so they weren’t designed to picture stars. Again, try taking photos of the stars with an old hand held camera and see how well they show up.