This is done purposely to:
A. Promote spending from players trying to get stronger quickly from having to battle higher "more expensive" players
B. Reward spenders with easier wins so they feel like their purchases were valid (we all know paying to win doesn't guarantee wins, this is how the system ensures they do - thus feel like they got their money's worth).
Sadly, it's been this way since beta, and although they say they're working on it, it's been over three years without a backbone game component which costs them so many players (but makes them tons of fast money). They don't care, of course, because the AI paywall has replaced us and they really only care about the people willing to pay multi-thousands to feel competitive in a free game.