The answer's been given a few times already but doesn't seem to stick.
Wild guess, and this is really disappointing if true: people don't see past personal identity. It's like, the simplest truth of Jungian theory, that foundational structures in your personal identity determine elements of reality that to you are necessary even as to others they are contingent. Like, the necessity of extroverting a particular kind of attention. Or like the necessity of distinguishing a particular inner world from the outer world.
That could be true... but I like to think that can be overcome to some extent if the person is open-minded and willing to question themselves.
Also the Ne users started it. They won't explain why objectivity is necessary.
Speaking of which, I have something to say about that idea of "objectivity."
I would disagree that Ne is an objective function. The most "objective" functions, if you will, are Se and Te. Both of them only work with and analyze data that's obviously right in front of them. You can't get much more objective than that.
But Intuition is inherently subjective. Even in Extraverted form, it still basically projects patterns generated by the mind onto the world around it. Those patterns do not reflect reality, but only assumptions about reality that may or may not be correct. Ni is not completely subjective in a way that Ne is not, it still gets the data it starts with from the outer world. The difference is that, after getting the data... Ni turns its attention inward, and looks at the pattern that has been called up. Examines the assumptions that have been made, and perhaps tries to look at all the different assumptions that could be made, seeing how those would change the pattern. Then, it can also extend the pattern into the future, branching out at various points when there are multiple possibilities.
Ne, on the other hand, just looks at the patterns that are generated, as they are generated, and either acts on them or discards them. The patterns are basically treated like reality, and trusted. Any analysis of how the pattern arose, or what assumptions they are based on, will be conducted by Ti or Fi, because that process requires an Introverted function.
Also, claiming that NPs are more objective because their Intuition is more focused on the object may be technically correct, but it doesn't mean the same thing as "objective" in the sense of being unbiased or clear. In that same sense, you would also have to say that SPs were more objective than SJs. Sure, they're more attuned to the object, they might be reacting to data that's available right now... but SJs are usually better prepared for the future, and tend to make better decisions in the long run! Also, SJs do focus on the present, they just respond to it in terms of how it relates to the past that they've experienced, and don't trust/respond to the new data immediately. It's not as though SJs don't take in new information.
And the same thing applies to Ni/Ne... Ni users don't trust or respond to new patterns immediately, just like Si users don't trust or respond to new sensory data immediately. This would make them "subjective" because they are primarily turned towards the subject, even though this doesn't mean that they're closed to outside data. They just focus on the internal impact and meaning of the information, rather than the external manifestation of it.
Se users and Ne users DO trust and respond to new data and patterns immediately, however. This would make them "objective" because they are primarily turned towards the object, even though this doesn't mean they are objective in the sense of having no biases or assumptions. They focus on what is manifesting in front of them, and how to respond to it, rather than on what it means or how it impacts them.
I have not been able to follow OMTs argument well, because he keeps making assumptions that contradict one another. My Ni cannot handle this well (nor can my Ti), even if the contradictions seem expedient in dealing with the external data. If he is saying that my inability to accept conflicting assumptions within the same context is a flaw that prevents me from responding to reality in the most advantageous way possible at a particular moment, particularly from a social perspective, or in terms of expressing my ideas to others... he might be right. But that doesn't mean he has the clearest picture of what's going on. I don't see where he's getting that from.