You didn't see apple implementing Samsung's "show your face to unlock your phone" feature because it was kinda slow and dumb. Likewise, I don't see any Android phones with 3D touch.
Yet when front-facing cameras came out, EVERYONE jumped on that feature, now your phone is dead in the water without it.
It was left to the history books the moment other manufacturers said 'meh, we don't need this right now'.
I went into the Apple store and couldn't even figure out how to get 3D touch to work and spent quite a while. After research it seems like you need to magically know which apps support it and even then which interfaces within the app. It is very obscure.
Apple is often first to market with new stuff, and sometimes I look on in jealousy (e.g. when Siri first shipped), but 3D touch is one of those features I never want Android to copy. I think it makes Apple's ecosystem worse and is opposed to their "simple and straightforward" UI strategy.
What were they thinking?
Several apps came out within days of the Apple 3D Touch announcement, such as https://play.google.com/store/apps/details?id=com.casual_dev..., that were installable and worked on existing Android phones. Since it was basically evidence of another Apple copy-paste, this information was basically ignored by iGizmodo / iVerge / etc, so many people think that Apple "invented" pressure-sensitive touch events, despite getting them a full 5 years after Android.
I believe that the reason that pressure sensitive apps were met with a "meh" on Android is because long-click works great and people understand it. Click to do a thing, long-click to get a context menu on a thing. It works everywhere, even on many Apple-developed iOS apps that haven't been "upgraded" to 3D Touch yet.
When do you think front-facing cameras came out?
The answer is, they were rather common in (non-touch) smartphones outside the U.S. before the first iPhone was even rumoured of, yet Apple only introduced one in the 4th generation of their phones.