The cost of running the rewards scheme must be paid. It is like a tax you incur. Also the cost for you to participate can be substantial in the form of time/attention. All for 1%-2% rebate.
Many rewards programs are also predatory in the way they want to sell your data so you are targeted by advertisers for products you wouldn't buy otherwise.
The recipients need to think about were to shop, switch cards once in a while, all extra work to get 1% back of the 2% that the card issuers extract from the economy.
Meanwhile in Europe the issuers are capable of running a profitable business on only 0.3% fees (and much lower for debit). So even though you may think rewards programs are nice, they are in the end costing you more, not giving you free money.
Many rewards programs are also predatory in the way they want to sell your data so you are targeted by advertisers for products you wouldn't buy otherwise.