Sans could teleport away again if he wanted to. It would be the smartest thing, with the way Greg is looking at him. But he doesn't, because there's something he needs to know.

"What's my fault, Greg?" he prompts, still on the ground with his hand clasped over his nose. His voice is flat and tired, as if already anticipating the response. He wants to know what was done to him, and if he can get any information out of Greg about it, even in the form of reasons for him to hate him, he'll take it.

Sans will take all the hate Greg can dish out. He can take it, he thinks. He doesn't have any pride to wound.