First, it's a known factor how incredibly powerful the card is in one-on-one formats
Prismatic Evolutions is a new special set featuring Eevee and its various evolutions along with new special illustration rare and illustration rare versions of various popular cards
In addition, you can explore using the new Map tokens, this gives you a little more flexibility over which of your creatures is exploring, which I think adds a nice new angle for the mechanic, and Im interested to see how it plays out
It mixes up a concoction of rarity, playability, and popularity of Pokmon
Prices move fast, sets keep coming, and good buying or selling decisions are made with fresh data, not with a rough estimate six months old