What's wrong with hair growing on your neck if it grows there? It's completely natural.
I know that this is slang/shorthand, but I don't agree with it at all. I work with plenty of people who have unruly beards and none of them fit the "neck-beard" stereotype.
I don't think it's a very nice term to be perpetuating. Judging people purely based on one physical attribute and then mocking them for it is not a great look for anyone.