The Socialist argument is that profit motives are fundamentally exploitative of workers, and that ownership over the means of production should be in the hands of people who work there. The reason why capitalism is bad is because it enables a privileged few to not work, by making other people do their jobs for them. This is why most Socialist law considers "social parasitism" to be a crime: work is a virtue.
The Anarchist argument is that work itself is the exploitation and that we should strive to reduce it wherever possible. The reason why capitalism[0] is bad is because it creates bullshit jobs that don't need to exist, not just that the workers aren't getting paid enough to do those bullshit jobs.
A good way to remember this is that Socialists gave us labor unions, while Anarchists gave us the 9-to-5 work day.
What seems to have happened is that /r/antiwork started off as strictly left-libertarian, and then gradually expanded to the sort of vague Internet Leftist consensus that we see today. This is a particular brand of left-populism that likes to use the word "socialism" a lot, despite promoting policies more akin to social democrats. There's an annoying quirk of populism (either side) in which they get drunk off justice porn and extremism and don't actually form a coherent political platform. It's one thing to say "I hate capitalism", and another thing to actually propose a workable reform or replacement. Reddit is particularly bad at this as the karma system encourages "content consumption" - i.e. the production of low-effort memes because that's what people upvote immediately. In a way, gaming Reddit itself is it's own bullshit job.
[0] I should point out that Anarchists do not restrict their criticism to merely capitalism but all forms of coercive power, up to and including Socialism as I have defined it here, as well as the Communism that the Soviet Union implemented. "Work is a virtue" is something shared across capitalism and Socialism alike.
