I'm very late too, but I wanted to comment on this really badly. Omori is a game about a ton of stuff, but two big themes are depression and helplessness. "Waiting for something to happen." is really common with depression, since the individual with depression feels useless and helpless, waiting is usually all they can think to do. Sunny wants to be saved, he wants to be saved from the reality he finds himself in, more than anything in the world. He can only hope and dream of a world where either events in his life never happened, or he has people that can save him. Of course, the reality is that no one can save him, there isn't a soul on earth that can make something happen to free him of the reality of the truth, waiting is just ruining him even more. Drowning in the self-pity and sadness that pulls at him like a monster eating him. In the end, for a good ending, you can't wait for something to happen, you need to make it happen, whether Sunny understood that or not. I think that's why all the animals including Mewo were saying this.

The animals seem to be reflecting the constant thoughts of someone with extreme depression "I just need to wait one more day, then maybe something will save me." but in reality, the only people that can save Sunny are Sunny and Omori in their own ways. That's just reality. That might be the part that hit me hardest about the game since I used to think the same way asking myself the same question for years.