In some countries, reporting yourself as single may be less common because the line between single and being in a relationship is somewhat blurry, at least for

In some countries, reporting yourself as single may be less common because the line between single and being in a relationship is somewhat blurry, at least for younger demographics, and people don't want to be faced with the awkward situation of having to decide when to change their relationship status. Easier just to leave it blank. Just pointing out it may have nothing to do with privacy concerns.