"A poster of our solar system where the sun and planets are at scale would look like a black piece of paper with a tiny white dot in the center."

Yes. And therefore a very valuable visualisation of reality.

Visualisations at scale are nice and useful, too, but they are misleading if the actual sizes are never shown to the target audience.

From what I remember there are various different depictions for different purposes. Most are just showing order and what they look like visually so the precise scale is a detriment and skipped. Most of the solar system to scale things I've seen in person are multiple blocks long so the planets are a reasonable size, there's not really a reasonable way to print a to scale in both size and distance in a book.

"there's not really a reasonable way to print a to scale in both size and distance in a book."

There is. Just one picture of small dots in lots of black space can give perspective, .. next to the other visualisations. And some books do that.

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