I just thought that maybe this is a response to a widespread experience of loss of control over life circumstances and decisions. You struggle for a while, then you accept and surrender to realizing you won't get rich, you will be forever at the whim of a landlord ... natrual reaction then is to establish a dissociated emotional way of life / thinking and conceptualize it - voilà Stoicism. You can't do anything about it so you might just as well stop complaining and worrying about it. If that works is another question and if that is Stoicism as it was meant originally also questionable - but I think this is the dynamic behind the Stoicism fad.