Deutsch didn't get morphed into Dutch.

It are words with the same origin, meaning of the people, the word people actually has the same origin as well.

Germanic people referred to themselves as Diets/Duutsch/Deutsch and some more variants.

The English mostly had contact with the Dutch, and called them Dutch, while the Dutch eventually started to call themselves Nederlands(Netherlandic) and only the Germans Duits. The Dutch anthem uses Duijtsche bloet, now Duitsen bloed (Dutch blood).

The Germans have kept the word Deutsch for their own, just as the Pennsylvanian Dutch (Deutsch).