Well stated, even when runescape'api' may be tightly locked down - they would soon run into precisely the exact same problem blizzard experiences. Lets say you would like to prevent plugins that auto-draw on the OSRS gold ground during boss battles, but also the'draw on x tile' API is also used innocently - you can't simply remove the API callback without breaking, and let us say manual floor markers.
Blizzard have not ever banned addons, with the exception of some addons which were trying to hide behind a subscription based pay wall. Short of anti-virus like code inside the sport that detects banned origin code, theres nothing they can do except split the API.
It was an unbelievable feat of technology but blizzard's only alternative was to cripple the minimap scope API it depended on - which is why range checking addons in WoW are cuffed to this day.
They can't buy it because it is open source and has been contributed to by hundreds if not thousands of people who have ownership rights of Buy Runescape gold their parts of the code. They can however just make their own construct they maintain and release without paying something, as it's open source.
Yep I really don't get why they don't do this , I wish they'd place the official connection on the site so people would not accidentally go to the wrong person.
There might be some NDAs involved and there's a possibility that it's similar deal as with wiki - that they pay x amount of money for labour and tools and runelite devs then have to do xyz and keep it operating.