Did you check the actual dimensions it would be?!

If you're being accurate in both distance and size scales your smallest dot would be Mercury and the distance from the Sun to Neptune (assuming this is a modern text book and we're dropping Pluto) would be 922000 of those dots. Even if we print it at the higher 1200 PPI [0] used for line art that's ~770 inches, that's a huge image far larger than any reasonable book. You could do it with a fold out but that's it's own expense and unreasonable for inclusion in an actual textbook.

That's why I was saying doing both accurate size and distance is difficult for the solar system.

[0] Images are more often printed at 300 PPI but I'm giving you the best case scenario here.

I was talking about rough illustrations with picture in picture (with a lense) to give a basic idea. But I do remember maps that could be folded out.

Most people have never seen a visual of earths layers to scale. The crust, even when thin, is usually not to scale