I would think that it would have something to do with either subtypes, or learned behavior.

I see ENFps regularly use EITHER Se role or Te (6th) whatever it's called.

In order for an enfp to use Se role, they have to inhibit/suppress their base function. This is akin to forcing something aside in order to use something else.

An enfp can also use Ti. To do so, the enfp would suppress their Fi and learn to use the Ti. This feels weird though, as if one is trying to paddle up a creek without a paddle.

In order for an enfp to use Te whatever (6th), there is no suppression occuring, they just learn how to utilize their Te to complement their Fi.

In essence, I think each type has certain options the individuals may or may not prefer.
1. inhibit F1 to use F3
2. inhibit F2 to use F4
3. complement F1 w/ F5
4. complement F2 with F6

I believe that personal experiences helps a type determine which methods they'll choose.