Not sure why you quoted my post, but I said for ME, I wouldn't schedule my wedding on a Sunday during football season and if I lived in the south where the SEC rules I certainly wouldn't schedule it during the championships. For some groups of people neither of those things would matter which is also fine. But here, in this case, it appears that if the bride and groom knew their guests remotely well they would know in advance this could be a pretty big deal/conflict. Would the couple prefer if no one showed up at the wedding?
ETA- The only reason I pointed out I was a woman is that typically men get "blamed" alone for this and it is not always the case.
I quoted you because you said "I never would have scheduled my wedding during this time." If you're trying to work around sports schedules you'll be harder and harder pressed to find a time where there isn't a time without some sport interfering throughout the year, that's a general comment regarding the premise of working with sports schedules regardless of whether you personally wouldn't it's bouncing off the idea of not scheduling during a sports season. Maybe in the south it's primarily football (approximately blocks out 3+ months) but translate that to other areas that have multiple sports that pull a lot of people and it would become messy.
MLB-end of March to close to the end of September (excluding World Series opportunities)
NFL-early September to early January (excluding playoffs and Super Bowls)
MLS-close to the end of February to mid to close to the end of October (excludes Cup matches), in 2026 because we have World Cup here they won't have any matches from May to mid July but World Cup is June through mid July) and their season will end early November (excludes Cup matches)
College basketball-mid October to early April (March Madness plus the Big 12 tournament is held here)
College football-late August to late November (excludes any bowl games)
For my particular area we technically have 3 different colleges people have a high enough fan base for but the seasons I mentioned are for my alma mater, one of the colleges people have a high enough fan base for is now in the SEC. College basketball has a higher fanbase than football for my alma mater in particular.
Outside of my husband and I we really don't know many Formula 1 fans but that season runs March-early December with presently 24 races and because it's worldwide the timing of the races is all over the place.
And to give an example of scheduling this past Sunday we had the last race of the F1 season which ended up being the deciding race for the driver's championship, we could have gone to our alma mater's basketball game though we didn't because of the other plans, and we went to our NFL team's game. All of those in one day.
All of that may be personally irrelevant to you but is used as a general point about working around sport schedules.
As far as the bride and groom knowing their guests that part wasn't made clear and the OP (being the cousin of the couple) may not know that answer either. We don't even know if the bride and groom had an issue with it so it's unfair IMO for anyone to make comments about the bride and groom negatively. At the moment this is just a guest who saw behaviors they didn't like and we are talking about it.