Maybe this is the issue? What you want is not same as what a user wants to see. Please, don’t be offended, but your point of view sounds very much same what webshops want to do with funnels: forcing a visitor to endresult what the shop wants because visitors aren´t doing it by themselves.
The obvious solution would finding out why visitors are not doing (clicking the bait, buying, what ever) but because shops think they know better, they take the short road.
If you are using something like announce category, and you don’t get what you want, there is two main reasons:
- your communication
- users just don’t care and/or bother
Using @everyone is just nagging. Like in domestic situations, that leads to two responses: target increases ghosting or walks away 
And… that is spamming. Not juridically, but mentally. You would send personal messages that are not personally. Massposting per forum topics is different thing because that’s why forum exists.
If you are using announce category and default is following it, most of users don’t change that option and they will see your announcements; if they respond is another story and depends of if they have same interests of the topic as you have.. Some will mute it, but it is something you just must live with, because it is theirs choise.