I’m not sure about it being exclusively beneficial to the industry (it costs developers to get their games rate), but I still see your point. Many parents don’t care about the ESRB ratings. But what are we supposed to do? Make the rating obnoxiously large on the box? Forbid the child from purchasing it? (Supreme Court ruled that you can’t).
Also, come to think of it, I’m not sure that the ESRB’s content ratings are the best. They give games with full frontal nudity a 17+ rating (not 18 plus, because that would be bad for marketing I guess), and lump them in the same category as “games with just a bit too much blood in them.”