right, you are asking good questions and thinking critically here, but let me explain to you why it wont be a problem

what you say is true of course but you have to consider that everybody knows if everybody does it, the network will collapse. so all miners will almost certainly not do it since then the value of their bitcoins would collapse. now theres always gonna be 5-10% of the population who will be greedy and not do it, but its basically prisoners dilemma, but with a twist where if EVERYBODY acts in their own best interest its actual in their worst interest, so incentive is extremely high to just forward transactions

even if you just consider pools as one miner, thats still a good 50-60 mining clusters plus everyone who gambles it up solo, market incentives is just too high for everyone to not forward transactions imo