1- Not enough content. DirecTV and ESPN stopped broadcasting their 3D channels in 2012 and 2013.
2- The glasses needed for 3D were clunky and annoying, and they made people feel self-conscious while wearing them.
3- 3D TVs were and are perfectly good 2D TVs, so 3D features weren’t often used.
4- 3D movies were closely associated with Blu-ray Discs as movie streaming started to gain traction.
5- 3D TVs need careful calibration and can cause eye strain.
6- Maybe it was always a gimmick. Ask yourself: Have 3D effects ever really impressed you or affected your viewing experience?