Sizing accuracy would definitely be an improvement, but it would shine a spotlight on the core issue that clothing manufacturers are hiding from consumers: they only produce hourglass shaped clothing and ignore the vast majority of body types altogether. If everyone’s sizing was 48-38-48-15 (bust-waist-hip-crotch) rather than L/XL/2XL, at least it would be a lot simpler to write a search engine for it — but there has, in the past century’s history, been extreme hostility from U.S. women in finding that their bodies are changing shape as they age, and so retailers are forced to choose between a sharp drop in profits by telling the truth, or making it difficult to cross-shop between different retailers. As no regulations exist around this, they appear to uniformly choose the latter.