As a long time fan of a soccer club that endured a decade of humiliation followed by success, the reason is that you can't tell the real fans from the fairweather fans during the good times.

So the bonding stories are often the ones where we reminisce about bad times and about players who were marginal in the league but memorable to us. Also the judas story works nicely too, that's always some guy who has to make a living and he ends up joining the rivals.

If you're going to find out who really loves the club, because you know tribalism, you can't talk about the time you won the treble. You have to talk about that time you schlepped your friends across the country only to see them get reversed 3-2. Or when someone does yet another shitpost asking for the all time XI, you pull out that obscure defender they got on loan who was terrible and played only 5 games. Or that time you did a pitch invasion thanks to a cult player scoring an equaliser in an otherwise bad game that people were already leaving.