K-pop bands tend to have lots of members (currently averaging 9) in a
group for not only better division of responsibilities between members,
but
to ensure a higher reach among the target audience.
Large K-pop groups can have subunit groups which would target specific
audiences divided even by their geographic locations. The larger the
group,
more diverse it might be in terms of looks, styles, hobbies,
characters, etc..
The more 'tastes' it might cover, the more members there are to love.