The reason it gets brought up is because the moment one person's needs or wants infringe on another's, there needs to be a way to decide who gets what. Generally, this is what people are talking about when they talk about various economic systems. You come up with different mechanics that use the distribution of goods to incentivize the production of more goods.
The only way we escape the economic games that need to be played, to keep people working and producing things society needs, is if we no longer need them to produce anything. Then you no longer need the incentives and feedback loops that tie consumption to production, and people are generally free to do whatever the hell they want.
The idea of post-scarcity brushes over that dark part of human nature, and assumes we can figure out how to cooperate, even absent antisocial misanthropes. In Star Trek, they have "figured it out", but the transition to post-scarcity is understandably only vaguely described.
Overall I agree with you: I'm not naive, nor am I a utopianist. I'm fine with more equitable. But we're so entrenched in the status quo that it feels like you have to talk like a revolutionary to get even a shred of "a little more equitable".
Edit: wait though what's a "post-scarcity" economy, anyway, concretely? I've heard since I can remember that we grow enough food as a species to feed everyone (and yet we throw tons of food out) - is that not a decent marker of being post-scarcity? We seem to have enough wealth in the US to be in neverending proxy or non-proxy aggressive wars against various groups of poor and largely non-white people - that wealth, used slightly differently, has got to be some kind of dent in all sorts of scarcity, no? I'm not writing this to attack you whatsoever; I'm genuinely curious. Post-scarcity is a phrase I've heard smarter people than me utter every now and then, and it only just occurred to me that I've never actually figured out what it meant. (I'll Google it now of course but I'd love to hear your perspective all the same. Cheers.)