I think part of the problem is not just recognition, but the fact that many people associate growth with something that occurs naturally or at least not as a direct result of single actions. Growing seems to be more of an overall side effect. So you eat food to grow stronger, but don't necessarily grow stronger from/by eating food; or you engage in marketing campaigns which will make your business grow, but you don't grow your business with marketing campaigns. And growing vocab sounds pretty mystical compared to 'increasing' or 'extending', but it certainly provokes the notion that our vocabulary is something to be nurtured and tended to, which, as a biological metaphor, isn't so bad, I guess. And it is a complicated process which is not just a case of adding new words and usages - so it has to be at least as applicable as growing businesses.
