But when can they do that?
They can't take an artist with them on tour. Comeback stages are only for the group. It is not like any other group has other artist with them when they want to promote their new song.
That only leaves end of the year award shows. In order to prepare for them, they need to spend time to rehearse and up until this year, BTS has a full enough schedule.
I agree that BTS schedule doesn't let them do much collab stages.
I guess this could be a reason why BTS doesn't get to perform with any female on stage bc they hardly do collab stages in general. Gender doesn't matter.