Having guides like qg is going to help them the need that they should have for them to overcome gambling problems that's hard to deal if done alone.
No offense to QuitGambling.com or any other service such as it, I believe gamblers who are highly addicted to gambling will barely be able to leave gambling and get rid of their addiction by merely reading some posts or watching some videos, especially if they are alone as you mentioned already. They might get motivated for a while, turn off their device, or close the gambling platform, but for how long? It can't hold them back forever and they will eventually start gambling again. That's why, for an addicted gambler to stop gambling, they need someone with them who will not let them gamble when they want to, in case they have decided to quit gambling themselves.
You're right because if prohibition could have been the way out to solve every gambling addiction then those that would have first supported this are the governments, because they wouldn't want the people to be that involved in gambling,
I don't see any reason why governments wouldn't want people to get involved with gambling unless gambling is prohibited within the country or the people are gambling with foreign platforms that aren't registered with the authorities in which case they won't be able to take taxes from them.