David Lovegood had been approached by several women since the death of his wife. After the first few, he could tell a mountebank from someone with genuine interest. The only problem was, there wasn't anyone with genuine interest. They just wanted his money, or to use him as another rung on the ladder as they climbed socially. He refused to socialize with any eligible witch then, and created The Quibbler.
After he published the interview with Harry Potter, he knew he had to hire someone for public relations to deal with the onslaught of owls and visits by Floo powder, so that he could continue to work on what mattered. He was extremely reluctant in hiring a witch that was so attractive, but she was qualified for the job.
Now that Luna had started her fifth year, he didn't want to distract her from her studies. He just had to find a way to tell his daughter that he was truly in love for the first time since her mother was alive.