Yes! I'd forgotten that.
That's the thing. Fans will join together on an issue that affects everyone. On single club issues they won't.
What other clubs fans who are shouting "you wouldn't have sold out / empty seats" here don't get is if (say Newcastle) get there next year they may get treated the same if we all don't stand together now.
I think on the Wembley issue, for the majority of fans, unless they reach a play off final, it is not sometimes that will affect them. This is because most finals are contested by top six sides in the premier league, or at the very least a premier league club. There is the odd exception, like Sheffield United this season for the semi final, but those occasions are becoming rarer.
If it's a side that hasn't reached Wembley for years then they won't care too much about the inconvenience of getting there and back, or the cost, they just want to be there as it's a rare visit for them. We were like that before we were always playing at the place.
Fans are too busy scoring stupid online points with other clubs to want to stick together. If only they did we would have the best prices, kick off times etcetera, but their own tribal mentality blinds them to this fact.