Rav Eliyahu Mansour addresses this question in his 5766 (2006) derashah on Parashat Mattot (link, starting at 45:55). He cites RaSh"Y (BeMidbar 32:42) who points out that there should have been a mappiq in the Heh of the word "לה". And that, without the mappiq, the word can be read "לא" (i.e. "לא נבח"). Because it can be read as such, RaSh"Y explains, this can explain why Novahh's legacy didn't last. But, "what's the lesson" asks Rav Mansour?
Rav Mansour then cites Rav Shimon Schwab who explains that there is a big difference between Ya'ir and Novahh. The difference is in how two different people look at their wealth. Ya'ir had a proper understanding: wealth is not bad, but wealth does not define a person's essence. A person possesses wealth; but, that person's wealth does not define him. That, explains Rav Mansour, is why Ya'ir calls his cities Havot Ya'ir. Ya'ir is Ya'ir and his cities are his cities; but, they're not one and the same!
But, Novahh had a different philosophy: he called his property Novahh, because he saw himself as being defined by his wealth; as being one with his wealth. That is why RaSh"Y says it can be read "לא נבח". Novahh's legacy didn't last, because of his warped hashqafah.
Rav Mansour cites a common and unfortunate occurrence today. Today, we ask people immediately upon having a short conversation with them "What do you do for a living?" And, based on that answer, we judge them. If s/he is a doctor, s/he is respected. If s/he works in sanitation, s/he is a zero. We don't judge people for what they are, we judge them by what they have. The guy can be a crook and can beat up his wife. It doesn't matter. We're not judging the person based on those things. We're judging him based on his wealth.
So, by mentioning Novahh only briefly (thus implying that his legacy withered away), the Torah is teaching us the crucial and eternal lesson that "it's not what you have; it's what you are that matters".