'hierom gaan wij niet' is also correct (duolingo thinks so too). But another correct solution closer to English would be: Vanwege dit gaan we niet
Does "Wij gaan niet hierdoor" also make sense? Every other sentence in this lesson has the "er" word at the end of the sentence
The rest of the lesson is dealing with location.
Phrased this way, what you are saying is 'We are not going through this.' - as in you are not going to pass through the indicated object.
Hierdoor has a connotation of a barrier.