How exactly do they make money? Coordinator fees?
Yes. They have claimed in multiple interviews and blog posts, including in the answers above, that they are being pressured or harassed to stop accepting certain inputs. We don't know by whom, when, why, or in what way, because they haven't chosen to answer those questions. They made it clear that the only two possible solutions to this in their view was to either stop running their centralized coordinator and therefore lose out on their revenue stream, or start surveilling their users and censoring their inputs. They chose the latter.
How is paying for some shitty service helping them with that?
By allowing them to continue running their centralized coordinator against the unknown harassment they claim they are facing.
Having said all that, they have also said on more than one occasion that they aren't actually being forced to do this at all, and this is a proactive decision on their part, so it is impossible for us to know for sure:
In a Bitcoin Magazine article, one of the owners of zkSNACKs Ltd., Bálint Harmat said the decision to blacklist was done proactively. While it is correct that there's no legislation that specifically says coinjoin coordinators must blacklist their customers' UTXOs, the challenges encountered operating the business in even the most liberal jurisdictions are numerous and multiplying.
But one other thing is that: if you, as a CoinJoin coordinator, if you want to work with institutional clients, hedge funds, insurance funds, Michael Saylor, and all these people, well, even if ZKSnacks were not to be regulated, those customers might very well be, maybe because they’re custodians of other people’s money or whatnot. And then these regulated entities can only become users of a coordinator—arguably, I’m not sure—if such a blacklisting is involved. Again, the major feedback that I got from institutionals regarding CoinJoin adoption was, I don’t want to mix with criminals—my compliance team is gonna take me apart on that one. Now, I don’t know if there is an actual concern here or if this is just, again, some preemptive speculative compliance, but arguably there is. So we might see this world where ZKSnacks specifically has a bunch of liquidity from institutionals that are just not comfortable to CoinJoin with another coordinator which has the Anyone can join policy, including criminals. And so there’s really a lot of nuance here. So yes, this alienates a lot of users—me being one of them—but also this will encourage a lot of new users to come in. And that is why it was a preemptive step from ZKSnacks, because the question was—I mean, we’re already really big, but we want to get even bigger—how do we not just attract more liquidity, but how do we also ensure that our legal set up will survive in the long run and we’re just not completely overwhelmed with court cases and things like this.
The second quote is also relevant to your second point, where they say they primarily want to cater to financial institutions.