I wonder how much of it is the variability to which different people are creatures of habit. Some people like sticking to the familiar in restaurants and foods, and others like trying new things.
Relatedly, maybe its the way things are slotted in ones head. If it is a D&D group or a bridge foursome or a chess club or... (pick one thing) then there is psychological momentum for that one thing. If it is a board game playing club or a card playing group or (pick a general type of thing) then there is a push to learning the new ones.
It probably doesn't take much to learn a new RPG - but it might take making peace with breaking a habit or fighting momentum.