On Java, at least, there is an occasional chat message pointing users towards their website.
Not to mention that in several channels in the official CubeCraft Discord, including the #info-questions helpdesk channel, there are plenty of links to the forums.
As an avid forums user, I too find it a bit upsetting to see that not many people make their way to the forums especially from the Bedrock community, but ultimately you can't force people to. Even if they were to register an account, not everyone wants to put in the effort to participate in the forum community. The forums follow a more professional manner, whereas Discord encourages casual chatter. Not everyone likes the former.
Well maybe some don't really care about the forums and just want to play the game by themselves or with their friends. I also think some people might think that they are getting spammed with the discord AND the forums so idk..
There is no reason for people to be upset over getting 'spammed' on Discord and the forums. People who register an account on the forums but don't talk will barely ever get notifications, and it is to be expected to at least get some notifications when registering for a website. I don't think this has anything to do with not many people being on the forums at all.
I mean that they think they'll be getting spammed in the actual minecraft chat
What does this have to do with it... xd