I think its primarily the "limited" number produced, which created the market and brought resellers. There wasn't a huge secondary market when Jordan came out, they had to build a brand etc. Eventually there was more demand than the number of products and reselling became a bigger thing. Also I put limited in quotes because a lot of the bigger runs are huge world wide. The main profit that is left is extremely small runs or the smaller sizes (which themselves have smaller runs). But just like a Black Lotus MTG card is just a piece of paper with some ink on it, they aren't necessarily just shoes, they're "limited" shoes.

>If it wasn't for the reselling market, there wouldn't be the same level of demand for sneakers

You can say that about literally anything. The value of anything goes up if it's liquid.

Not quite. The spread narrows if it’s liquid. All else being equal, a liquid asset is preferred over an illiquid one, but liquidity does not mean something is more valuable.

It just means the price paid or received is closer to the consensus valuation.