You should. You shouldn't. That's all some people do. Tell YOU what they think you should or shouldn't do. Do you do what they say?

I always wonder if they lead just barren dull empty lives and that's why they are always looking at the plates of others.

Could be.

Why don't they learn to keep their eyes on their own plates and make sure they are in order first before venturing to tell people what's wrong with their plates?

A question that probably can't be answered.