This was after Jesus came back from the grave. A few of the women had told the disciples He had risen. They didn't believe their testimonies or the words of the two men Jesus showed Himself to on the Road to Emmaus (Cleopas was one of them).
When Jesus appeared to the disciples, He didn't even mention them running away before He died. He didn't mention them being overcome with fear. None of that surprised Him.
Their refusal to believe was what brought His reproach on them.
God understands we are dust. He is never surprised we stumble and fail at times.
But when we refuse to believe, I believe it really disappoints God. He knows it's hard to do at times when everything we see looks like it is against us. He wants us to overcome that, look with the eyes of faith, not the eyes of sight.