I am expecting it is because MM5 defaults to having no backups. The user needs to know that it is there, that it is not in the place they probably expected (Tools>Options), and that they are exposed to loss (play counts & playlists) if they don't turn it on.
Compounded by the fact that the Getting Started material is really poor, and is not in your face when getting started.
touche. Acknowledged, but then ... isn't denial at the core of every Hoarder.
I notice that you sidestepped the main point. ie whether a minimal backup scheme should be defaulted to on.
I think that Ventis is letting their customers down by having it default to off.