Yeah, no, you're right... I spent like 10 minutes typing something "creative", rereading it, deleting it because it wouldn't be as creative as I thought, and then starting the cycle all over again. :`) This is why I try not to reread my posts...
Also, you have to mention that there are other factors other than that. If you meet me in real life, I tend to reflect more of my Fi and Se, because I really don't feel the need to use my Ni (other than art class). But online, especially in forums that require more intellect, I tend to pull out my Ni and my Te because I don't think Fi and Se are fit for what I have to say. (Although if you do look close enough, there is a hint of Fi and Se hiding behind the things I type.)
I'm not too sure, but I feel like people use their tertiary because it's the closest thing to who they want to be and is obtainable. It makes sense that you become what you look up to, and, being humans, most people look up to something they lack or they aren't that good at. And usually, if it's too hard to get, we don't try. We think (or at least from my experience) "Oh, that's just who they are and what they're good at. I'm never going to be like them." Not too sure, but I view that our inferior function is the function we lose touch of the most. It's like trying to touch a bird without lifting yourself from the ground. Maybe with enough patience you can touch it, but for the majority of the time, it flies away. So, you try something like a cat. Still hard, but it seems more doable than a bird. So we start admiring the tertiary function and start working towards it, and if we admire it, maybe others will as well. As much as we would like to say that we don't care, especially when it comes to first impressions, we try to show others at least a little bit of what they might admire. (Unless you forgot that other people's viewpoints exist) when in reality, we would show our true selves in front of people who are close, which is our dominant and secondary functions.
Sorry if it seems confusing. I'm pretty hungry right now and I have a hard time thinking straight when my stomach is about to take control. If anyone needs a bit of reassurance, than feel free to asak questions and criticize because woops! Didn't mean to seem all over the place...