That's very odd. This command will export the values of annotations in the file. It's actually not possible to limit it to just one page...
I'm running it as an action on Acrobat Pro DC. No annotations beyond the first page are exported if I run it on multiple files.
Would be helpful if someone could confirm the same for them?
Strange. What happens if you run the code manually, from the JS Console?
Bernd: That's the issue. Acrobat won't even load the annotations unless you force it to by using syncAnnotScan() first. I've run into this before with Actions.