export multiple stickies

The only way I know -

Open the stickies.

Open a new, blank TextEdit (or other word processor) document. Leave it open to one side.

Make a sticky active, press Command-A to select all its contents, then drag that selection into the open document. Do each sticky in turn that way.

Why?

I don't know why.

Like just about all folk who respond in these forums, I don't work for Apple. For an answer to that question, you'd need to contact the Apple employees who made that decision.