I think of Reddit as a 21st century forum, whereas Facebook is a true 'Social Media' website. Forums have different usage patterns and allegiances compared to social media websites. They can be roughly compared, but it's a poor comparison, like trying to say if Excel (reddit) or Powerpoint (facebook) is better.
Facebook has groups which sort of function as forums, but they're crudely spliced into your news feed, and rarely(!) sorted in chronological order. Forums on the other hand have dedicated threads about specific topics, are easily searchable and a two year old thread can still be relevant.
Social media sites tend to be more immediate, and comments on old posts may only continue for several days on average.
TL;DR Reddit and Facebook are very different products, with different usage patterns, and have different appeals to different segments of society.
It does not surprise me in the least that an internet forum would have a lower daily usage count compared to a social media service.
Facebook has groups which sort of function as forums, but they're crudely spliced into your news feed, and rarely(!) sorted in chronological order. Forums on the other hand have dedicated threads about specific topics, are easily searchable and a two year old thread can still be relevant.
Social media sites tend to be more immediate, and comments on old posts may only continue for several days on average.
TL;DR Reddit and Facebook are very different products, with different usage patterns, and have different appeals to different segments of society.
It does not surprise me in the least that an internet forum would have a lower daily usage count compared to a social media service.