Pokémon Diamond and Pearl are both WAY slower than Platinum. In particular there’s just a delay between every action and Pokémon losing health in battle is excruciatingly slow. Mostly fixed in Platinum.

Scarcity and some artificial scarcity called grading. Take for example Pokémon vintage trading card game packs. Base set has a bunch of print differences but even buying a normal unlimited version pack is $300-400. The value of a Charizard, if you pull it out of that pack, is ~$200-400 raw. However, if you grade it and it comes back a 10, it’s suddenly “worth” $1000+.

This is not quite as prevalent in video games but it is happening. The price of popular Pokémon games that are complete in box are sky high because someone somewhere wants to buy it and submit it for the chance it’s “worth” 10x the price.

Pricecharting.com is your friend. Patience is a virtue.