Moving from mono sound to stereo doesn't require anything of the listener. Going from black and white to colour doesn't require you wear special equipment.
But 3D? You have to put on special glasses which you also have to remember to charge. Oh, and you can't look at other things while you're using them.
There were some passive 3D displays (the Nintendo 3DS and a few early Android phones) but they required the user to stay in exactly the right position, or the illusion was destroyed. So you couldn't easily share the experience with a friend.
Until we have TVs which can shoot lasers directly into our eyeballs, I think the barrier to entry is too high.