The money they collect is the money we pay them minus the money they pay us. If we can't pay them more the only way to get more is for them to pay us less. Gross simplification obviously. Then the typical strategy is to blame immigrants or Jews or whatever for the decrease in living standards, and crack down on anyone who tries to improve things.

Edit: this is sort of a meme-ified version of the tendency of the rate of profit to fall which is the real theory of how economic crises in capitalism come about and not really the same as what I'm describing here, but along some similar lines. It's worth reading about from actual scholars in detail if you're interested in that sort of thing.