Post scarcity societies can't be approached in any meaningful way with modern economic theories.
Star Trek is neither socialist nor capitalist, as both are systems designed to manage and portion out scarcity, and are based on economic theories that lack any predictive abilities in systems that don't work in a context of scarce resources that need administration.
Neither the labour theory of value nor marginal utility theory make any sense when all resources are trivial to obtain for individuals and whatever resources your community uses can be reused virtually endlessly within the limits of entropy.
Are we really dealing with "scarcity" at this point?
Supermarkets throw away literal millions of tonnes of food annually. "Reduce, reuse, recycle" has become a hollow mantra that cannot be truly adopted by the profit driven design philosophies of consumer products. Sustainability is being treated like some chic perk rather than a critical topic that must be taken seriously if we want any hope for our futures.
All these things are profoundly capitalist problems. Of course, it's not like marxist-leninist 'experiments' fared any better, devolving into their own variants of capitalism, but there are many other socialist ideologies to consider (such as anarchism...)
We are, because people want luxury goods too. Post-scarcity is about being able to produce most goods with barely any human labor (would absolutely be true for food if every person on earth only worked in food production or to produce machinery needed for it), which we aren't even close to. AI and automation might get us there (though it's questionable when the cycle of just investing the newfound labor capacity into more luxuries will stop, if ever), but people are actively resisting that (reasonably so) because the current economic system basically everywhere is horribly rigged towards funnelling the excess wealth to rich individuals rather than improving the living standards of society as a whole.
Idk, I'd say we want quality goods, and are lead to believe that these desires can be fulfilled by the lofty luxury goods market which is founded more on artificial scarcity than material scarcity. Even when rare materials and expensive labour are involved the fact that this simply makes them "more valuable" seems more important than any actual need, or lack of alternatives. Meanwhile, affordable products get enshittified, shorter lifespans, etc.
though it's questionable when the cycle of just investing the newfound labor capacity into more luxuries will stop, if ever
Which is precisely why "post-scarcity" can only be reached with actual societal change, not just technological advancement.
While that may be true about Star Trek after the fact, the truth is that in order to get the federation off the ground, and the world economy in line to create the first Enterprise and crew and all the scientific advancements they made, required the entire world moving to a purely socialistic platform/agenda to achieve.
I don’t think you can discount first contact’s affect on that shift. Finding out you’re not alone in the universe would surely have a massive societal impact.