I'm pretty sure Mafuyu excludes himself. He thinks he can't do it, so he turns away. He thinks he can't fit in and so he doesn't try. Yuki, Hiiragi, and Shizu accepted that about him and didn't push.
Uenoyama does push but not enough - he doesn't know how to get through to Mafuyu most of the time. He had to grab Mafuyu and scream at him way back at the beginning to get him to sing. But that's not really acceptable behavior, to yank and yell at your bf all the time. Besides, Hiiragi and Shizu were just telling him that Mafuyu needs time to think it through - so he's giving him that space.
They are wrong though - Mafuyu needs help. At least now he's willing to find that help. Kaji will help, hopefully.
Honestly, I've never understood why Hiiragi, Shizu and Yuki never included Mafuyu in their band, even just to come and watch their practices. They all knew he liked music, especially Yuki but they just excluded him from their circle, which led to the issues between Mafuyu and Yuki. Now its happening again and they (Hiiragi, Shizu and Ue) should know better. Stopping repeating past mistakes and communicate.