Just one for Gaster this time.

Well, there were several reasons telling the group that he had reset was not in our study's best interests. For one, you cannot take someone's word as proof in a scientific study. Second, let us say that they did believe Sans; then the whole group would try to reset. Can you imagine how disastrous that could be?

Also, while I hold Sans in the highest regard, he is also a, erm, prankster, I think is the term I have heard some of the researchers yell at him. So you may be overestimating how much his colleagues trust his word.