It just occurred to me, as I cleverly averted not-cleverly putting my silk tie in my lunchie burrito. I said, Whew! Good thing my tie didn't get burrito gunk on it! How would you even clean a tie? I don't think you can. So you throw it out; but wait! Throw out silk? Maybe you could recycle it into smaller garments. But what's smaller than a tie (aside from a smaller tie, smartass)?
And therein have I reverse engineered my answer.
In the days when silk was imported from the far (much further back then) east and therefore very expensive, you couldn't just throw it out! But yet, you couldn't wear the evidence of the last week-end's drunken debaucherie. So you recruit the royal taylor to make something out of the non-stained portions of your garment. What's best to make with an uneven swatch of fabric? Some kind of modified scarf. As fashions drive themselves, the scarves got more and more ornate, as did the knots used to drape them. Soon, they fell into the complex knot patterns that make up today's ties. As the fashion spread to the masses, the shape was made to conform for purposes of mass-production and conformity itself.
Now, because some medieval oaf couldn't hold his liquor, we all have to wear them. Next time Friday rolls around and you think about loosening your tie to have a drink, remember that the alcohol is only tightening that tie...
Hmm... I like that. It sounds more and more plausible the more I think about it. Ford knows; I might be right.