Evidence has shown that access to a parser doesn't improve the vast majority of a player base. Bad players will continue to be bad, despite evidence showing just how bad they truly are.

If nothing else, World of Warcraft is an excellent example of this. Addons are almost universally embraced by that community, and people STILL pull garbage dps. People have had access to parsers in WoW since Vanilla, that's ten years of garbage players not improving despite access to a resource that explains, IN DETAIL, how garbage they really are.

In fact, that's my point entirely, you can lead a horse to water, but you can't make them drink. There are VOLUMES written on optimal gearing, stat weights, theorycrafting, rotation, openers etc etc.. Some people spend countless hours providing knowledge to players who will never read it. If a bad player wants to improve, the knowledge is there for them, and if they don't? No amount of in-game resources will change that.