The incentive to not act like the slackers is how it impacts your "network". It's pretty insufferable to work with these people, when the success of your project depends on them or their team for whatever reason. If our team is hiring and I see a former coworker got laid off who was a slacker I won't put in a referral for them. I guess it won't impact them much, because tech is still growing and demand exceeds supply…
> [they] say their new goal is to be “perfectly mediocre.”
Note that mediocre is not the same as slacker. It is impossible to distinguish a genuinely mediocre developer from an intentionally mediocre one, so no, it won't impact their network unless they are really careless and tell everyone that they can in fact perform better.
Do you stop talking to a colleague because they have never found a security vulnerability and fixed it?