actually you can make a perfectly useable living hinge with an fdm machine.
BUT you need to use the right material and make it around the 0.2-0.4mm thickness.
Some of these materials are amazingly strong and tough.


I'd stack a living hinge made from colorfabs xt co-polyester filament against anything you can make with injection moulding.

And obviously the stiffer flexible filaments like polyflex can do it with inpunity.
I'd always use two layers as the slicer lays the second layer down across the first so you get a very tough final material.

But I must have spent 5 minutes bending the xt 1.75mm filament backwards and forwards and it just couldn't care less.
While it is very expensive stuff - it's my current favourite material.