@kornboi imo, it's a rule that's enforced irregularly, but it gives a reason to kick out guys who are being disruptive. There was a reddit thread who translated an employee who said more detail:
[ul]Preventing upskirt photos (voyeurs especially liked to prey on women who were doing the drawing thing on their purikura b/c they were distracted by the screen)[/ul]
[ul]Preventing nampa/pickup artists and assholes from disrupting customers[/ul]
[ul]Keeping out hosts who are trying to "steal" customers (according to OP, the two industries are 'competitors' and one store he knew hired security to keep hosts away)[/ul]
[ul]Attracting more female customers (game centers don't need to advertise to gamers who will come anyway, so this is how they stand out)[/ul]
[ul]Attracting more couples (because the guy will definitely pay for the purikura and then maybe try to win a UFO catcher prize or whatever)[/ul]
from https://www.reddit.com/r/japan/comments/549ecz/men_alone_or_in_maleonly_groups_denied_service_at/d8012fp?utm_source=share&utm_medium=web2x