Two Reasons

The Dawson wasn't a noble family like Harmon or Kelly or Rivas. A middle-class family who came to fame overnight without effort. 

The rich heiress from the Baldwin family falls for the secretary of her father. Afraid of her father stopping her, she elopes with her lover with the help of her lover's friends. However, fate had a different choice for her. Her lover stepped back at the neck of the time. Incensed, The heiress grabs her lover's friend and gets married in a church. 

And that friend was a son of the Dawson family.

The heiress manages to convince her parents, apologizing to them. And the son-in-law had to settle in the Baldwin family. Being treated like a doormat. He endures for a long time.

Who doesn't like money and power?

That's when Leon comes into the picture to help the son-in-law. The elders meet with an accident and the son-in-law becomes the master of the family.