There have been two theories that were floating around pertaining to the fact as to why the 3D was not rolled out more widely by Apple. The first being the fact that it has got poor yield rates. Due to this, it reduces the system production to a large extent due to the fact that this particular feature can be a real expensive thing to add. Another reason will also be the fact that due to this, the company would have withheld from the fact that its iPhones are cheap.
Another thing that could be a challenge is the fact that that the 3D Touch for large screens would require significant changes. This is also one of the main reasons why, it has not yet been seen on bigger iDevices like the iPad.
Though, this is yet to be confirmed, however there does seem to some ground of truth in it. There have also been situations where the behaviour of the company has not made sense. The question is still left unanswered as to how be it that the very feature the company backs up is not yet added to the iPad.
Even though there are various challenges pertaining to the manufacturing front, however that still does not stop it from being used effectively by a lot of iOS users. Today there are also a lot of apps that are being developed which supports the 3D touch feature, however there are just a few that is yet to adopt this feature. If you look at the app store, then you will get to see that it has a separate section for the apps that are specifically supporting the 3D Touch. As of right now the count is believed to be around 56 apps however it is believed that this number will rise up.