Maybe someone else can explain a little better than me since I am not the best at theory by any means, But in my opinion using the pentatonic scale it is easier to use and a player does not have to worry as much about note choice to make it sound good, therefore it appeals a lot to people beginning to solo (like myself). When using the natural minor scale it makes the note choice matter much more and it is harder to make it sound "good". I'm sure someone else can give you a much better answer but that's my take on it