3D Touch was a big UX problem, there was never a way to show the user that you could do it and where you could.
Apple has a problem with discoverability in quite a lot of features. There's many small little things in iOS that users don't know about and likely will never find out about, perhaps because they want to keep the UI clean.
See, I didn't know that, and I've had iPhones since the 4 (a grand total of four devices), and am the sort of person who reads the manual in general, and likes to know all the features of a device I spend time with.
On the one hand, thanks for the tip! On the other hand, Apple has an enormous discoverability problem, it's getting worse, and they're responding by making the UX dumber instead of addressing it head on.
Tips is actually a great example of how Apple fails at this/discoverability. The tips in there are novice and below level at best. With none of the advanced features even discussed, let alone more obscure or hidden ones.
Apple has a problem with discoverability in quite a lot of features. There's many small little things in iOS that users don't know about and likely will never find out about, perhaps because they want to keep the UI clean.