Ten (edit: even five!) years ago I'd agree with you. Back then a source control system was a piece of software you used for keeping a versioned history of your work and to enable you to collaborate with coworkers or friends. It was a tool.
Now? It's A Big Deal to a lot of younger developers. It is almost totemic. If it's not Git and (ideally) Github then.. it isn't worth hacking on?
Long answer yes with a but. They will eventually take up the mantle from devs who age out or die. We might have something totally different than Git at that point but it's not good to dismiss them either. That is how projects die.
Now? It's A Big Deal to a lot of younger developers. It is almost totemic. If it's not Git and (ideally) Github then.. it isn't worth hacking on?