I assume you mean in the secondary market... The ATACR has been our best selling scope model this year. Last year, it was S&B. They are well performing world-class scopes and perhaps the pervasiveness in the market means you see more. I know of nothing negative about them. The 1-8x and the 7-35x are best sellers in their market, and the mid and longer range models are selling steady, and all perform fantastically.
From a resale standpoint, I think NF holds it value better than most.
For the most part people selling ATACR's are selling versions with outdated/underperforming reticles such as the MILR, now they NF finally offers a decent non tree type reticle (mil c) people are trading out for those update reticles.
I've seen quite a few NF ATACR 5-25 F1 scopes with the TREMOR 3 reticle listed for sale or trade, specifically for the same model with illumination, since the USMC adopted the illuminated version along with the Mk 13. Just as some have to have the latest and greatest, some have to have whatever the military is currently using. I'm not saying there's anything wrong with that, I'm just offering a possible explanation for some of the recent volume of ATACR's listed for sale.