Because he's a creep

Besson's second wife was actress and director Maïwenn Le Besco, whom he started dating when he was 32 and she was 15 after having met 3 years earlier.[43] They married in late 1992 when Le Besco, 16, was pregnant with their daughter Shanna

Le Besco later claimed that their relationship inspired Besson's film Léon (1994), where the plot involved the emotional relationship between an adult man and a 12-year-old girl (played by then 12-year-old Natalie Portman).[43] Their marriage ended in 1997, when Besson became involved with actress Milla Jovovich, then 19, during the production of The Fifth Element

Edit: And the multiple rape and sexual harrasment claims