So when people go to the Aviva to shout for Ireland or whoever, they are not involved in some sort of cultural event? Culture in the broad sense, even the part of the event that is just the fans wearing colours etc? I presume you mean re-the players. I would say that players at all national sporting events have some link to some cultural factors, examples of which have been given by others above.
Anyway I think the issue here is about players being "required" to wear poppies, for the reaosn that if they didn't, they would be indicating disrespect for the national service people, who did their duty for their nation, in which the event is taking place, and who are being commemorated.
I'm sure there's clear precedent, from the rugby matches for example? No way both teams can be expected to wear an emblem like that. An armband maybe. By choice.