Because the amount of exp and skill points you get don't depend on where and what monsters you fight, but on the level of the targets (while random encounters everywhere fully scale with you) and the actions you perform
Ive mentioned earlier that playing many colors in your deck is good because youll have access to more cards
This gives the game a huge number of combinations
It can mean defending yourself with Propaganda, Elephant Grass, or Sandwurm Convergence, or maybe the criminally underplayed Wall of Souls
(Want to hose Flashback, try in-set Catalyst Stone, of any color, and it helps your own as well)
More often than not, a little bit of the price spike will carry over, making cards steadily more expensive over time