I'd say it's closer to real estate than a parking spot... Think of a book store that has a great business but it is located in the middle of a bar district. At some point the property is more valuable than the business and it makes sense to sell it so someone else can develop a business that better leverages the location.

Except you do not own it, you rent it. Most folks who sell domains just pick one up for a few bucks and try to charge a ridiculous fee to transfer it. You are taking a publicly available address and extorting someone who actually intends to use it.

That is by far the best explanation, better than I could have said it myself. Thank you, you nailed it perfectly.