First, it seems tacky scrounging for peanuts from the users' captcha work. Or it's like a product/services website showing Adsense ads. It's a cheapening message to send.
Second, since you make more money from more captcha volume, you're incentivized to maximize your use of captcha which is at odds with every complaint in this comments section about captcha. Most sites only use captcha to gate low-volume actions like register/login (e.g. HN).
They created their own Ethereum token too which always puts a bad taste in my mouth these days.
Finally, it doesn't address the upstream complaint that someone else is profiting off the user's "work" rather than the user. Though I don't find that complaint very reasonable. And a tiny fraction of a cent sounds about right. The truth is that users benefit from anti-abuse systems. The number of bots that HN's recaptcha on register/login has stopped is worth that tiny fraction of a cent to most users.