First, Colt stopped making them ca. 2007. With stopping production, comes scarcity in the market. The Python action was hand fitted; like no other revolver. The Python has a finish (Royal Blue, nickel) which was far better than any other Colt, and to some, superior to other manufacturers. That mystique remains, and it drives up the cost of the remaining market. What could be purchased for as little as $400 new, now commands prices in excess of $2000, and the price is not going down. One only has to decide when, or if, to jump into the fray.
The Colt action was unique. It continually "stacked" until the sear released. The S&W, on the other hand, stacked up to a certain point, and then used the same amount of pull to release the sear. Folks generally line up on one side, or the other.
The barrel on the Python has a tapered bore, which greatly added to accuracy. That's why the
Smolt conversion (Python barrel, K frame) was a popular conversion. You just never see a S&W barrel, and a Colt frame. The Python is also larger than the S&W K frame (and the attendant problems with light .357 bullets), smaller than the N frames. That was a selling point.
The Python was a status symbol especially for some police officers. Carrying one denoted an elite status, if you will.
No one person can possible corner the market on used Pythons. There are thousands out there, and some folks won't sell their guns at any price. That's the way markets operate.
There are also niche markets within the general market. 2.5" and 3" models bring a real premium, because they're scarce within the family. The most common barrel length, 4" does bring the least money (relatively). There is a lot of fakery out there,too. Just look at the number of fake boxes, documentation, "California Combat" models, etc., that are for sale. Folks will pay a premium for the accoutrements.
I own three, and they're great revolvers.