Why aren't all Blu Rays now 3d/2d combo Blu Rays?

[tripletopper]

With so few releases at home coming on 3D, and most 4k releases include a Blu Ray, and sometimes even a DVD, why can the Blu Ray be a 2d-compatible 3d Blu Ray?

If you play it on a 2d Blu Ray or 4k player, you get a 2D movie. But if you put it in a 3d Blu Ray or 3d+ 4k player, why should it not ask "turn on 3d mode? Y/N"

It's sort of like turning off the chroma key on Colorized movies for pure B/W fans.

Also it doesn't ask whether you have a Dolby System or DTS system? I wish it did, because my headphone surround system depends on what discs are inserted in the Xbox One. But if you have no surround system, it just defaults to 2 track stereo, or even mono if that's all you have.

I think I can answer my own question. Ever since August 2011 when Parma Oh protested the 2012 Super Bowl being 3d only, 3d has become a 4 letter word.

Why don't movie makers have 3d as an unadvertised hidden feature in the blu ray copy of a 4k set? If 3d really is a 4 letter word, but movie makers want to release a 3d copy, why not do that? Will the 3d haters really be righteously riotous and call for a boycott?