Comment by delroth

The main reason is that these days every rare collectible card in Pokémon is an alternate version of a cheaper card from the same set. For example, N's Zoroark ex ASC 286/217 is a $120 card, but the same set has a more common, mechanically identical $1 card numbered 137/217.

This is very much intended so that collectors chasing the nice full art / textured rare cards flood the second hand market with the less desirable cheaper versions. Players can then easily buy those cards for almost nothing and with ample volume available.