Your language.
Probably out of respect for his family he has built up to this time, knowing that he would be attacked mercilessy, just as he is now experiencing, and they would be affected. The older kids are now in their 30s and are well capable of handling the business; and his younger children are up and going -- Tiffany is in law school and Barron is around 9 years old. He and Melania have had a good chance to spend time with him.
Have a look around the web site of the Trump Organization. Being POTUS would be a step down and a great personal sacrifice; many think his run is just ego; but he has a lot to lose, as you will see if you take a good look. There are some good videos of his children at the link called "The Next Generation."
You may have heard him mention that he has often given money to people running for office; or his prank early in the campaign of having people call Lindsay Graham on the phone because he had his number on a scrap of paper, saying Graham had just been in to ask him for money. Those large donations have given him the opportunity to sit down and talk with many lawmakers and policy people; and he has written 15 best-selling books, three of which are his ideas about what the country needs: The America We Deserve, Time to Get Tough, and Crippled America.
Here is a video of him testifying before the U.S. Congress 25 years ago regarding regulations affecting real estate development, the construction industry as a whole, and even low-income housing.
He also says in his testimony that he was invited to testify before Congress by the chairman of that committee. The chairman was Frank Guarini of New Jersey -- a Democrat.