I think it’s a number of things.
First of all young people just don’t seem to use old fashioned forums as much as older people now do. They use Facebook and reddit, so I’m told, and probably other stuff I don’t even know about.
Plus this forum seems to have drifted to the right, collectively and as individuals. Maybe that’s just because people have got older.
Plus JWs themselves are older on average, so it makes sense that the people who leave tend to be older too on average.
Whereas the young ones who leave JWs these days, some of them seem to just walk off without much fuss. No angst about doctrines such as mediator or 1914 or all that. It probably seems quite archane to most young people these days, inside or outside JWs.