They don’t earn that much. At most 0.25 BTC per block, and thats the fee paid for an entire block if someone wants to fill it up with spam at 40kb each UTXO at the rate of 25sat/vB, which is already more than average fee rate. It is not average Timmy working 9-5 who wants to spend 0.25 BTC to add spam, its entities with money behind them, and what could their motives be?