Absolutely nothing, if the site members wants to stop old threads getting new posts, then damn well lock them, otherwise don't whinge when people post relevant remarks even if it's an older thread.
I fully agree with you, why have a zillion threads all with the same type of content. And I think it's especially poor to harangue a guy who just finished a cnc machine build, that's a hell of an accomplishment, and should be commended.
cheers, Ian