When playing physical card games like Magic the Gathering or Pokemon, you are constrained in who can play against due to the physical nature of the cards. The "best" decks you play against are your friends and other players around you, unless you are at the point where you are specifically entering tournaments.

I know when I played for a bit back during my school days it was just me and a couple friends who did it fairly casually, so there was very little pressure to spend lots of money to build a great deck. And if someone did try to spend tons of money we probably would have harassed them about it anyways.

The problem is nowadays, due to the online nature of these games, is that you aren't just playing with friends and other people near you, you are playing with anyone who happens to be online. That means you are much more likely to play against people with good decks who spent lots of money building that deck. So the pressure is much greater to also spend money.