Since you ask so nicely ... sure!
The first part is primarily just that it is my personal preference. Much like I like the color green, but cannot give a logical reason supporting my like of this color, neither can I give a logical reason supporting my personal preference. ^-^
Now, I can hear the counter-argument : "If you don't like appearance tabs, then you don't have to use them!" To a certain degree, that is true. However, I DO have to deal the consequences of seeing OTHERS make use of the feature. Seeing a Lancer running around wielding a giant fork does impact on my view of the game world, whether I choose to make use of such a feature or not. Even worse, seeing fulled armored gladiator in a Santa Suit.
But, that is merely personal preference. It doesn't really count for a lot, except in my recording my personal "vote" on the matter.
Now, what did Yoshi-P have to say about this:
Now, from a purely mechanic sense, it is clearly not the case that appearance and stats need to be linked. I'm granting some amount of "Lost in Translation" here, and am thinking he is saying that appearance and stats should be linked in his view. Games like DCUO, Aion, and the upcoming game Secret World show that item appearance can be unlinked from item stats.
However, DCUO and Secret World are different genres (superhero and modern), and the inclusion of this game mechanic in Aion very arguably made the setting feel "less fantasy". Whether you think this is a "big deal" or not is a matter of personal preference, not right or wrong. However, it is Yoshi-P's vision that will guide us here:
Bold added for emphasis.
Final Fantasy is a fantasy setting. This means that there are certain conventions, a theme to the world that the development team is trying to establish. This in turn requires certain limitations on the completely free expression that you are shooting for. Other settings may not require them (e.g. superhero, modern), but Yoshi-P and the development team feel that the FFXIV setting does need them.
To use a very crude analogy, a person has freedom of speech (in the U.S., anyhow), but that freedom does not extend to slander, or the ability to yell "Fire!" in a crowded movie theatre.
So, if SE were to allow the separation of the gear appearance from stats, they would lose their ability to maintain the sense of visual theme that creates their vision of Final Fantasy XIV.