I agree with you on this that people can change wife, religion and other things but when it comes to teams that they support they find it really difficult to change as being a fan is something else infact there are people who don't eat simply because their teams loses a match and one this about football clubs that I have seen is that they all have season's that they play well while some other seasons they struggle some even go into relegation so you don't expect your team to be on top for ever as no one can remain a champion forever so when your club is not doing well it's expected of you to still keep Faith on them just like the good Old days when they where things where good
Sometimes I wonder why it is so difficult to switch football clubs. These clubs do not pay their supporters, and they do not force people to support them. People are also not required to take any form of oath before supporting a team, so I am curious why it is difficult to change teams.
In some cases, even when a player who inspired a fan to support and love the team is signed by another club or retires, the fan's loyalty remains. This is really surprising, but it is our reality. As you mentioned, even when the team is having a bad run of form, die-hard fans will continue to support them despite numerous criticisms.