Could be a multitude of reasons for some people, I had one which I bought from you LOL, no longer do, reason being is I am shooting trap more.
1) Weight, I hear that a lot. For me it was not an issue, I shoot trap and the guns are heavier.
2) This gun likes to rattle itself loose, from the front sight to the forend end to the charging handle, best thing to do is loctite all screws before using. Keep allen/torx keys with you when shooting.
3) Accuracy, trying to freehand it at 25 and expect a nice/decent group is not easy, that could be contributed to the perceived weight. Hitting a steel plate, well that's easy.
4) It kicks more than one would expect.
5) It's really fun to shoot and easy to burn ammo at the range, with the rising cost of ammo it may be slowing people down.
6) It's a low hanging fruit, semi-auto centre fire could be on the chopping block?