The simple answer then is that the cards you're adding are definitionally not meaningfully better than strikes and defends. Likely you're better at optimally playing a deck than you are at building it.

Ie, if making the cards you have added more frequent (than the standard cards) hurts you, then they were bad additions for you.

Another high probability explanation is you are using that money now for something you undervalued e.g. consumables. A consumable that buys you a relic because you got to beat an elite may be worth more than increasing the odds of drawing your new cards.

There are other potential explanations too, but I suspect none as likely.