But as I said, "People have managed OK for decades...". What percentage of football fans travel by train? I bet it's less than 10%. Most will walk or cycle (home games in your own town/city), others will drive (or be driven) or use a supporters coach. These are all available on Boxing Day.
Just as an aside to that, I didn't attend my clubs away match at Old Trafford this Boxing Day just gone as there were no trains. I have no access to a car and travelling by official coach is of no interest to me, so sweeping generalisations like yours aren't really helpful. If I had really had wanted to go I could have got the coach but chose not to for my own reasons as I don't like getting driven straight to the ground and dropped off and hour and a half before kick off. Like to have an explore, take some refreshments under my own steam.
Also fans of certain clubs don't always like in the same town or city as the club they support so local train services provides the means to get to games. My club draws support from small towns nearby like Brighouse, Mirfield, Elland, Wakefield and Dewsbury, 4 of the have direct trains to Huddersfield to bring fans in.