In large part it was because of a debt crisis:
In 1933 the Newfoundland legislature voted itself temporarily out of existence, ending 79 years of responsible government. The following year, Newfoundland accepted a constitution similar to those in place in the directly-controlled Crown colonies. A country voluntarily giving up self-government is highly unusual, yet many other societies also experienced a loss of faith in democratic institutions during the Great Depression of 1929-39. The roots of the fiscal and political crisis that led to the collapse of responsible government can be traced to the First World War.
Here is much more. Don’t expect this model to be repeated anytime soon.
Hat tip goes to Joseph Cotterill.