Hellor Dr. Ram SIngh, I think it is purely because of lack of information about ResearchGate among them. I hope there should be some sensitization about ResearchGate and other similar tools to the scientists engaged in academic/research activities in the area of Geography, etc.
Thank you Dr. G.R.athinasabapathy , may be u are right. but they should fallow research gate so that other geographers can see their quality of research out put.