A market requires scarcity, because scarcity is what neccesitates trade.

You can't invoke market mechanisms to defend a post-scarcity scenario.

Why would the ai owners make things cheaper or even available at all once their abundance machines give them everything they want?

What would they get out of if it? What could ordinary people trade for it that their abundance machine can't give them already and that would be worth giving up their monopoly on productive force?

You can't argue "this will change everything" and "this is how it's always worked" simultaneously, and yet AI accelerationists bring out both to defend their ideology.