taboo, nuff said.

In my opinion it’s the fact that there wearing somthing when they don’t need to and it covers nothing plus on them it makes them look a bit cutter so bam

Socks not hot for me. Just makes them cuter. :3
 
But the concept of clothing being able to make them sexier than without is easily explained. Just think of BDSM. What’s hotter? Nothing or leather and fishnets?

This is hardly an adventure in the comments.

@Background Pony  
Only if you don’t think about what you read.

I have to say, all your answers sound really stupid when actually written…

I thing it might have to do with the simple fact of trying to be sexy by doing something differently than normal. If they were wearing sock all the time, maybe it wouldn’t be that way but just thinking that someone made an effort to look appealing is sometime sufficient to put the mind in a receptive state.

Socks/stockings are hot on both humans and ponies because they emphasize the legs without actually showing them. It’s a mental thing. Strategically covering up part of the body can be more exciting than straight-up nudity. That goes double for ponies – they don’t usually wear clothing, so covering up their legs makes them even more teasing and tantalizing.

@Background Pony  
Preference and fan-based depiction. Not much exists in show, but when the fandom finds one little thing it explodes in popularity mostly since it so deviates from the usual of this being a show targeted towards those around the age of 7. So the fandom is partly to blame, the other part being the inherently cute nature of the show that attracted people to it in the first place. From there it’s pure imagination, constructed either out of jealousy for being unable to be there themselves or fascination with the subject in question; for the most part, it seems to be a combination of the two.

It is sexier to take something off than it is to start with nothing. Anticipation is the name of the game, and nothing is payoff.
 
Then again, considering ponies are naked anyways, it’s almost a moot point.

@Background Pony  
“How can anyone find humans arousing? It’s basically the same question. From an objective POV there is nothing more attractive about humans than there is about ponies.”
 
But you aren’t objective; you are a human. People find other people attractive because it is necessary for the proliferation of the species. True, people have weird aberrant behaviors all the time, but your statement is pretty much gobbledegook.

Are you Jon Snow?  
Because you know nothing.

Maybe http://tvtropes.org/pmwiki/pmwiki.php/Main/TheissTitillationTheory comes into play somehow?

@Background Pony  
Soft, innocent creatures that are as beautiful inside as they are without? Plus the inherent sexiness of the equine form?

@Background Pony
 
Because they are beautiful and sexy. How can anyone find humans arousing? It’s basically the same question. From an objective POV there is nothing more attractive about humans than there is about ponies.
 
Ponies, on the other hand, are actually drawn in a way that emphasizes many wonderful things. Their large, expressive eyes. Their beautiful hair/tail. Their ample hindquarters and their symmetrical frame.

The better question is how can anyone find ponies arousing in the first place?

The problem I have with (most of) those explanations and the discussions I’ve seen elsewhere is that they explain why clothing in general can be better than its lacking, but not why socks are the most popular for the particular purpose of enticingness.
 
This question has quite bothered me for a while.

Because you are used to seeing them without clothing. When things become so commonplace, they lose their enchantment.

@Psychopomf  
That’s basically it, though I don’t get this one very much.  
I think AJ’s hat renders the concept much more.  
Or Octavia’s bowtie.

@MaggieXawesomeness  
Agreed.

Because they normally wear nothing. When they’re wearing something, it’s like they have something to hide. Something naughty. And that’s pretty hot.
 
That, and irl it’s way more awesome for a girl to leave something on during sex. Waaaay more awesome. Especially if it’s a skirt.
 
Hmm…need more skirt ponies…

Meh, not hot, just cute as heck for me

Same reason some mean find woman hotter the sexy outfits then nothing at all, sure a naked woman is hot but sometimes having something on is far sexier.

I. . . don’t know O-O they just are.

Because, irl, the more a woman is covered the more specialized things become.
 
In Victorian England, seeing a woman’s ankle was considered sexual.
 
Similar principle.