They were one of the top teams in the 70s when I was a kid making my "favorite team" decision. Didn't hurt that I lived in SoCal at the time (Edwards Air Force Base in 3rd & 4th grade, Luke AFB in Arizona for 1st and 2nd grade before that - when AZ didn't have a team.)
The other reason is that the Dodgers were my mom's favorite team. She grew up in Ogden, so a lot of the Dodger greats went through Ogden on their way to the majors. And, as a young girl she had rheumatic fever, so she would lay in bed at night and listen to Dodger game broadcasts.