Let's be real, most of those who write on forums are seeking to get money, whether through signature campaigns, bonus distribution, airdrops, etc. This, of course, is not a bad thing unless it turns into spam to get rewards without providing any valuable content.
Until the emergence of social media, forums were the best place to exchange opinions and experiences, discuss, and obtain information, but after the spread of social media, this changed. Therefore, I believe that obtaining money from forums is the strongest factor that makes them continue until now. Of course, it is not the only factor, but it is the strongest factor as I mentioned.
Even if the mixers and signature campaigns disappear from the forum, I believe that there are still many opportunities, even if their returns are less, but they are still acceptable to maintain activity in the forum to some extent. Members will remain active waiting for new opportunities.