well there are 3 reasons i'm a broncos fan who was born and raised in los angeles
1) we lived near where the raiders had their training camp in oxnard. it was ‘84 or ’85 and we went over to watch them practice. i was trying to get an autograph from a player who was leaving the field and he told me to eff off. nothing big and he probably wasn’t even talking to me but i was 7 or 8 at the time and i decided i no longer liked the raiders
2) my dad was a browns fan. and while watching afc championship i started cheering for the broncos to tick him off. yes that was "the drive" game.
3)i read a book about running backs for a reading thing at school. one of the people the book talked about was tony dorsett. i’d already kind of decided the broncos were my team but then dorsett played his final year in denver. since i’d fallen in love with him while reading his story that kind of cemented my choice for favorite team.
stuck with it even with the blowout super bowl losses (wins/losses never really affected me one way or the other) and it’s been over 30 years now.