Yeah it is a limitation of Ubisoft's API. They don't display the achievements on the Ubisoft Connect website either, you can only view them in the desktop client, and even then, only for your profile. If you have a user added a friend it doesn't let you see their achievements in the app either. Until they change this, no way we'd be able to pull the achievements.
I'm not sure why they don't make the achievements more visible, it's been like this ever since the early Uplay days, but hopefully more changes will come eventually.