I don't like them for the same reason I don't like tiny baby boys in bow-ties or any of the other accoutrements of the adult world of fashion, show-biz, etc. They are infants and children for such a short while and should be free of those 'trappings' to wriggle, kick, crawl, roll etc, until they begin to show an interest in such features and objects. Not to mention the danger of suffocation from such items, or choking if they put them in their mouth.
Maybe I have a too 'romanticised' view of infancy and childhood, I'll admit. However, these trends are to satisfy the parents I believe, nothing else. No baby girl without hair is bothered by the fact of not yet having much of it and little boys barely able to walk aren't the least bit interested in looking cute for our benefit in a bow-tie. It might be 'fun' for a photo-session, but apart from that it would be nice if babies could just be and look like whatever they look like. For a while in their infancy, it won't even matter whether they're boys or girls. Not to them, anyway. A contented baby smiling at you from a pram or buggy is a delight, regardless of which sex they are.