Miners still have to choose to include your tx. The risk of losing during two blocks being mined goes up as blocksize does (longer to transmit across the network), so you still have to incentivize the miner to include your tx.

Ofc there will be miners who make much larger blocks no matter what, but it comes down to how urgent is your tx?

...because miners choose whether to include a transaction or not. Obviously they have no incentive to include a zero fee transaction

There would be an equilibrium where the fee is worth the marginal cost of mining it

Unless miners start colluding their strategy will become "include every possible transaction with fee greater than $0." which means fees will settle at the smallest possible value greater than 0.

Yeah sure, everything I buy costs the smallest possible value greater than zero.

shawabawa3 already explained it "There would be an equilibrium where the fee is worth the marginal cost of mining it"

The miner has cost X and wants profit Y. He adds those together and now the price is X+Y. Someone wants his transaction on the blockchain, he is going to pay X+Y unless there is a miner that offers an even lower rate.

You're making the assumption that the block reward is high enough to make transaction fees irrelevant, which is a trivial observation and not what we are interested in talking about here.

There is no cost to adding a transaction to your block if its size is uncapped. Once a miner completes a block why wouldn't they maximize the profit they can make on it?

If we assume no blockreward then the fees will be whatever motivates miners to include your transaction. If the fee was zero, then no miner would even bother.