Because people were loving his solo journey. And he went back we probably wouldn't get his and stain pair-up. And I think it's stupid for him to be influenced by them, when his mentor wasn't able to stop him. Plus, he is much more capable for them to fight alongside them. He kinda don't need them. Hori is yet again derogating him for him classmates involvement, which I don't find nice.
I actually don’t think he should go back right now. He’s still not ready and I agree he needs to get stronger by himself. He needs to get to a point where he can be sure he can protect his friends and people he cares about. They all need to train hard. When they are all strong enough then Deku can go back
Bro cmon deku better not join them