Anubis doesn't target crawlers which run JS (or those which use a headless browser, etc.) It's meant to block the low-effort crawlers that tend to make up large swaths of spam traffic. One can argue about the efficacy of this approach, but those higher-effort crawlers are out of scope for the project.
reminds of how wikipedia literally has all the data available even in a nice format just for scrapers (I think) and even THEN, there are some scrapers which still scraped wikipedia and actually made wikipedia lose some money so much that I am pretty sure that some official statement had to be made or they disclosed about it without official statement.
Even then, man I feel like you yourself can save on so many resources (both yours) and (wikipedia) if scrapers had the sense to not scrape wikipedia and instead follow wikipedia's rules
wait but then why bother with this PoW system at all? if they're just trying to block anyone without JS that's way easier and doesn't require slowing things down for end users on old devices.