It's just not this forum or even generally Amiga forums. The same drop in in users and activity is happening across all the forums I know of/visit/member of/etc and that covers a lot of forums on tech/family/pets/cars/trucks/martial arts/computers/Amiga.
Other social media platforms are a bit the cause, but even the modern social media special interest groups don't have the activity of the forums of old.
Just in my option from my own observations.
One of the biggest issues is that younger users don't have the interests in formation and discussions of topics of interest. Popular social media platforms are not conductive to lengthy discussions across multiple topics. Try having a conversation of length on Twitter, Snapchat, Instagram, doesn't work well, and it's those type of "sound bite" platforms that are popular.
Another large reason I find, is the ageing of the population that made up forum users. One, as we all get older, have families, other responsibilities, priorities change. It reduces the amount of free time available to hobbies/interests/forum participation/etc.
Another reason it user population attrition. People's interests change, hobbies change, and people leave behind the things that used to interest them. Related to this is, and using the Amiga as an example, how many people of younger generations are taking up Amigas to use? They are few and far between.
