If it created trails, then it would also multiply the brightness of the stars and the comet by the number of pictures (17 in this case). Each satellite appears only on one photo, while the stars and comets appear on all 17 in the exact same spot. The only way to stack them to get a normal looking stars and comet is to make an average. And since the satellites only appear on 1 out of 17 they would effectively disappear.

Unless you actually want to have the satellites there, then the stacking would just cut the region with the satellite from each photo and simply glue them together. That's how you can get this image.

I actually just tried it in Hugin. Normal stacking from 2 pictures by default made the objects that appeared only on one of the pictures semi-transparent. If I did this with more pictures, they would be so transparent that I wouldn't see them at all. But I could manually select a mask to cut out the portions that I don't want. If I select and exclude the object (satellite streak) it would disappear completely. But I could also purposefully include the streak and in that case all the satellite streaks would be included in full brightness in the result. That's most likely how this photo was made.