Why do people ask if they can 'help' you when all they really want to know is what you are doing? Why not simply ask "what are you doing?"

sometimes you just need to get good at delegating, say sure, and quickly assign them a very specific task! try it!

To be polite

True that. Funny but true lol

You do certainly need help.

What are you doing?

People usually ask that trying to appear as though they care but when you hand them a list or even ask one favor that could actually help the look on their faces tells the real story.

Do they go away when you say “no”?

I don't know.
I'll be honest I don't go around asking everybody if I can help them, but if I know they need help and I ask I sincerely mean it.

Can I help? is often just the fancy version of “I’m curious.”