That can only happen if the higher density coincides with equal economic growth in the neighborhood. Otherwise, the higher density could result in a negative home valuation trend.
Given the above uncertainty, and higher density could result in more traffic, noise, crime, nymbys are likely taking the correction position for wealth preservation and quality of life.
"Traffic" doesn't come from higher density, it comes from zoning bans on mixed-use neighborhoods which force people to drive everywhere. The "crime" argument is especially silly: why assume that higher density only ever attracts criminals? Usually, having more people around is a positive.
You can assume higher density has "more crime" because the increase in people means if you want to keep the same absolute rate of crimes (which is the only thing people ever notice--every violent or sexual crime will be repeated in the news), you have to correspondingly increase the efficiency of crime-fighting, and American police aren't up to the task, even if they were motivated to do so.
Given the above uncertainty, and higher density could result in more traffic, noise, crime, nymbys are likely taking the correction position for wealth preservation and quality of life.