For me, a lot of it is the fans. You also likely grew up with every little sh*thead supporting Man Utd; as someone once quipped, "He supports United in place of having a personality." Idiot fans who don't know the first thing about football, and would stop supporting them if they ever had a bad patch.
Given that most of us are in our 20s/30s/40s, Chelsea and City still have a decent contingent of fans from before the glory days. In my lifetime it's never been like that with United or Liverpool fans, and certainly not Arsenal fans.