A possible answer: from HItler by Ian Kershaw, p. 820. ( I see no direct primary source for his assertion but it makes sense.)

"As long as Hitler had a future, he had ruled out marriage.. His life, he said, was devoted to Germany. There was no need for a wife. It had also been politically inconvenient. No one outside the inner circle was to know of Eva Braun's existence.   She had been forced to accept that she was no more than an appendage, there when Hitler wanted her to be, stored well out of sight for the rest of the time.....The marriage cost him nothing. He did it simply to please
Eva Braun, to give her what she had wanted more than anything at a moment when marrying him was the least enviable fate in the world."