I see, the last time I looked into this was shortly after apple closed the last known jailbreak options and before they allowed jits in some circumstances.
The lack of a speed difference I assume is down to the fact that delta supports some pretty weak consoles which you could emulate in a browser. Dolphin's jit vs interpreter vs cached interpreter in for example Wind Waker is a 10-40x speed improvement on my phone.
JIT is not disabled on the hardware level, safari does use it for JS for example. Just ordinary AppStore apps can’t do so.
Also, in my experience with Delta playing some of the Pokemon games, I noticed no difference between the non-JIT and JIT-ted versions.