Hina needed Yui to cum here as well—physically, not just mentally—so their connection could deepen and become truly pleasurable.
At the moment, Hina and the others couldn't really feel Kouhei in their bodies. Not enough, anyway.
Because it was only Yui's subconscious that was actually feeling all the intense pleasure, her physical self could sense it too—but only faintly.
It wasn't the full-blown wave that rolled through her mind and soul.
And that limited connection wasn't strong enough for the others to cum, no matter how much they tried.
Yui needed to reach climax here too, in the real world, to let the full intensity ripple through everyone connected.