Why were the citizens of washington, dc, not allowed to vote in presidential elections until 1961?

They did not have any electors to represent them
In the Congress, there is no representative from Washington D.C despite the fact that it has more than the required number of residents living in Washington D.C. This is also because Washington D.C used to be a District of Columbia. Aside from that, the Washington D.C used to be the home of many African-Americans in the United States. In the 1801, the people were given the rights under the representation of Maryland or Virginia but were stopped because of the Organic Acts. It had been a struggle for the Americans living in the United States.

Possess private property.