They've just very cognizant of not giving away more information than strategically necessary. They like to be one step ahead of everyone.
Amusingly, when you actually correctly call out their motivations, they do everything they can to discredit your claims because they're threatened by the idea of a loud-mouthed extrovert blabbing their secret plans to everybody.
This, I think, is one of the biggest reasons INTJs dislike sharing their deepest feelings and ideas with extroverts, especially EPs. They don't want the whole world to hear about it!
As far as I can tell, giving away way too much information when it's not strategically useful seems to be one of the biggest INTJ criticisms of ENTPs...am I right, Z?
As Jaguar always says, preference =/= skill.
I don't think all introverts are deep people; I do, however, think all introverts prefer to focus on depth over breadth. Whether or not they're actually good at it is another thing entirely.
Are there introverts with very little depth? Sure, but they still have a preference for focusing on depth, even if they suck at it.
Some Fe users (especially NFJs) consider the entirety of humanity to be part of "the group" and thus will pretty much do anything to help anybody, but this seems to be the exception rather than the rule.
Anyway though, I'm talking about the way Fe users derive morality, not their habits regarding helping others. They look for a moral standard that can apply to everybody equally and uniformly in any context--Fi takes issue with this, as it feels that generalizing moral standards circumvents individuality and freedom of expression, freedom to do what feels right to you, no matter what "the group" thinks.
Fi doesn't like that because it squelches the personal freedom that goes into deciding what feels right to each person individually. Since Fe considers morality in terms of an externalized standard, though, giving up this individualized depth is fine because it allows to agree upon a universal standard by which everyone can be judged consistently.
Think of it in Te terms, since you are a Te user--when it comes to impersonal ideas, you want to establish a collective consensus based on externalized evidence; that way we can all get on the same page about what standards of measurement to use when we discuss impersonal ideas. Te doesn't really care if this removes the degree of theoretical precision that Ti prefers, because Te thinks impersonal ideas should be dealt with collectively and according to an objective standard, while personal feelings/morality should be dealt with privately by the individual (Fi.)
FeTi inverts that. It's doing exactly the same thing, just the other way around--in FeTi's view, morality/ethics is something we should all collectively agree on, while impersonal ideas and logic should be dealt with privately according to a subjective and individualized perspective. Fe shows breadth by giving up the depth and complexity allowed by Fi's personalized treatment of ethics in favor of coming up with a collective, one-size-fits-all moral standard by which everyone in the group can be consistently judged.
Unfortunately we have to make that moral standard fit everyone in the group for Fe to accomplish this, so the degree of personalized depth that Fi prefers is no longer possible. In Fe terms, morals need to fit everyone, not just you personally.
It's just like how Te wants impersonal ideas and theories to be externally demonstrable in a way that can make sense to everyone, not just you--and this is why Te users constantly insist that Ti users provide more externally verifiable backing for their ideas. But asking us to do that is like us asking you to provide external evidence that your moral opinions are objectively correct, which completely defeats the purpose!
You say: "I feel that this is right for me." An Fe user says: "Oh yeah? Well you need to prove objectively that your moral viewpoint is shared by a majority of people!" But that's not the point for Fi! Fi and Ti are both inherently personalized, so they don't understand why Fe and Te constantly want them to use external means to prove their validity. For Ji, externalized proof is completely beside the point.
As an ENFP, when you look at something from an Ne perspective, you are favoring breadth over depth.
When you switch it up and look at it more from an Fi perspective, you are then favoring depth over breadth.
If you are a balanced individual (and it sounds like you are), then you'll be able to use aspects of both at the right times--sometimes breadth is more useful; sometimes depth is.
The fact that you an extrovert means the Ne breadth focus comes more naturally to you than the Fi depth focus, but it certainly doesn't mean you're incapable of focusing on depth!