I think it ultimately comes down to most convenient and least terrible. Like McDonald's is not good by any stretch of the imagination, but they're everywhere and you mostly know what you're getting. I find that some locations don't know the difference between a chocolate shake and a chocolate malt, and if you ask for the former, you always get the latter. Why McDonald's even offers malts is beyond me (malts are superior to shakes IMO, but not everyone likes the grainy texture... if you know Maltesers or Whoppers candy, it's the stuff inside, but powder, that's malted milk, and making shakes with malted milk (Malts) is awesome). But I've only been to two that do it. (Maybe they just ordered the ~~wrong~~ right shake mix.)