If a person would ignore one part of a license, they may also ignore other parts.

... Then why would they care that it's ND?

Not really. You're supposed to attribute the original creator. And if I did make major changes/additions I'd find some way to flag that. But you don't have a Github-style change log.

Not really, but you can't just distribute a changed version as if it were original. That's just as illegal as if it were ND.