Grandad People, be they men or women, are drawn to Gransnet by seeing a conversation that they would like to join. These conversations are not started by the admin staff, they are begun by ordinary members who have a question or an observation, and they continue when someone replies, someone else answers that reply, ageeing or disagreeing, and it proceeds from there.
The Gransnet forums are a grass-roots phenomenon, not one created and designed by psychologists for a specific social engineering project. It is up to individual posters to initiate threads that attract readers and/or posters. If you want more men on Gransnet, then you will have to start up threads that they will want to join in with, on subjects that attract them, and then keep adding to the conversations, in a way that encourages men to reply to you and develop the debate or the chat so that more men then join in. If there is a need and a demand for men to chat online in a friendly way, then they will be drawn in, but you can't just demand that someone else does it.