From the discussion of anime genres

You do not understand the essence of harem. Harem should be homogeneous - the girls in such a harem love not only the main character, but also each other. Such a harem is resistant to the rejection of any of the members, even in the case of leaving the protagonist, it will not collapse.
The centralized harem, assembled only around the protagonist, is not stable, generates conflicts and a bunch of other problems.