I don't think it has anything to do with the folder, it's the apps that aren't showing notfiications. I don't know about Google + but my Facebook messenger app does show the notification count
I'm guessing it has to do with whether the developer adds that functionality or not. Facebook seems to have added it. Unfortunately, badges aren't usually an Android thing so other developers haven't.
If you really want notification badges, you can get Apex Launcher and Apex Notifier. Better since you can change themes too.
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