Users want their transaction to be relayed to miners.
Miners want the transaction to reach them so they can earn the fees associated with those transactions.
Miners want other miners to receive their blocks to have their reward recognized by the network.
Users want to receive the block the miners produces to they can know the state of the network.
I submit that pursuit of just these policies would actually encourage centralisation. A small number of large miners will consume fewer resources than a decentralised mass. A single trusted data centre could be even more efficient.
Can you define decentralization/centralization in this context?
Sure. By centralisation here I'm referring to the gradual reduction in the number of block-generating entities. To be clear, I claim: absent a block-size limit, this centralisation process would occur naturally and that a good relay bandwidth market would accelerate this process.
Always happy to be proven wrong; just want to give you something more concrete to work with.