Part of the problem with the perception of guards is that it sometimes feels like you just plug in a mountain of a man and call the position filled. LTs that can't move go there and that drops the prestige a bit as well. What qualifications exist for guard that makes that a goal for someone to strive for? You could be strong as they come but if you're athletic as well, you'll be an RT or, if you're very athletic, maybe a LT.
So how many good-great tackles would've been all-pro guards if they'd been moved inside? Instead, they had some athleticism so they got bumped outside. For example, see Albert in KC who everyone gushed over as a guard but he's been a solid LT instead.
It's kinda like the special teams of the OL. If you were better, you'd be playing elsewhere.