Star Wars fans, why didn't princess Leia send R2-D2 straight to her father on Alderaan instead of to Obi-Wan?

In Star Wars episode IV: A New Hope she sends R2-D2 to the planet Tatooine to seek Obi-Wan and display a message revealing to take the plans to her father. Why didn't she just create a message for her father and send the droid straight to him?