Why is the past participle disappearing?

I know, I know, languages change organically, yadda yadda yadda.

Bull.

I was going past a restaurant, and they had a sign in their window that said, "Close." Close to what? Eh? What they meant, of course, is "Closed."

Or the everlasting "first come, first served" issue. "First come, first serve" is nonsensical. The verbs ought to be roughly parallel; this formulation implies a tennis match.

If people just thought, a little tiny bit, none of them would come up with phrases that drive me insane. Can't they have a little compassion on my nerves?