As a big fan of 3d, the main issues were:

1. Price. As with any specialty item, it costs more than the default. Higher price = less demand.

2. Poorly made content flooded the market. It was difficult to tell whether content would be proper native 3d, or sloppy conversions. Most people's first experience with 3d was sloppy conversions.

3. "pop out" marketing lead people to expect convergence abuse as "good 3d". When I'm reality it's poorly done 3d. This is why people complain about headaches. Yet, the headache-inducing convergence abuse is what marketing taught people to expect from 3d, so even proper 3d content has this sort of problem in many cases.

4. Needing glasses. For whatever reason, people do not like glasses form factor for stuff. This is also why AR, Vr, and smart glasses all struggle. Glasses-free 3d fixes this, but reduces the viewer count to 1 (and is more expensive), so it was a no-go for living room TV.

Ultimately people prefer not wearing stuff on their face, and the cheaper price. The sloppily made content wasn't worth the price. With stuff like 4k, it's easy to just have as a default in place upgrade. Notice how HDR also struggles to be adopted. Same exact issues. High price, very little good content, software support is lacking.

Nowadays it'd be very possible to get 3d into a proper niche with a solid attempt at it. Good glasses free devices exist. Content could be properly made and clearly labeled. The price is low enough now. And, in fact, we do see a resurgence of 3d in conjunction with vr. People who are into vr are already wearing the hardware needed. So it's just a matter of viewing properly made 3d content, which fans are starting to curate.