I think the problem is that it's not available everywhere on all mobile devices (Android, iPads and older iPhones don't have it) so it's not utilized well or im

I think the problem is that it's not available everywhere on all mobile devices (Android, iPads and older iPhones don't have it) so it's not utilized well or implemented as much as it could be, nor is it a universal behavior users can internalize like they do with panning and pinch to zoom. Android somewhat mimics it with long pressing, but iOS also has long pressing as well as 3D touch. Without ubiquity it can't become a primary UI mechanism, only tacked on to something that must work without it. Personally though I don't think 3D touch is any less discoverable than your right mouse button on a computer. If you have a 3D touch capable device you had to configure it at least once when you got a new device capable of it so you know it exists just like you know a right mouse button click state often exists (Macs don't even ship with obvious right-click capability, the OS has it disabled by default and neither of their mouse input types have an obvious right click mechanism just by looking at them)