He knew that if he wanted to ensure that he was able to take them down completely he would have to take proper measures and had to be certain of what he was doing.
He needed an army for him to be able to fall back on and that was why he was doing his best in order to make sure that he had garnered all of the men and that he had them in his arsenal.
But he knew that even if he were to explain that to Diana she wouldn't fully understand.
They wouldn't able to see the vision that he had planned and what he intended. They would most likely push him away and think of it as nothing more as the mere ramblings of someone who had not been able to think past his delusions.
That was one of the reasons why he had chosen to keep his plans it himself because he didn't want them to go on and end up refuting him.
However the other reason was that secrets didn't remain secrets for long and they were able to travel very fast.
