Bitcoin has a KYC problem. We don't know any customers. One man's spammer is another man's marketing genius.
This plays into how Bitcoin software handles transactions that are gossiped to it on the network. Your local node does a list of anti-DoS checks, as well as miner compatibility checks, caches the transaction, and forwards it to any nodes connected to yours.
For miner incentives, this is not exactly straight forward, but easy enough to inuit. If you can "make the mempool better", you accept a new transaction, and kick out whatever it replaced.
This isn't the whole story. What it it makes the mempool contents better for miners, but is worse