I'm pretty sure it's got to do with their parents as well. Sena's angry comment strongly points in that direction, and the discussions between Reina and Makino (and the fact that Reina was letting herself get blackmailed over how she expects her parents to react to learning she's lesbian) are very strong support.
Just curious if it will end up in a "they should have been open to their parents earlier" way, or in a "parents get btfo because their daughters chose their girlfriends over them".