Different countries have different customs when christmas celebrations are at their most important.
In Germany for example Christmas Eve is when our celebrations peak. And on Christmas Eve alone you may spend an extensive amount of time having Christmas dinner and opening presents.
Depending on your family traditions there could also be additional activities such as singing, having coffee and cake, talking walks, going to church if you are religious, having extended family over, etc. etc., or even just Christmas movies, yes.
In many cases you also don't get much time off during the day because you (have to) spend a considerable amount of time preparing for said afternoon and evening activities. Esp. as an adult I'm not gonna let my mum and grandma do hours of cooking and decorating while I'm having fun playing video games. (Not saying that's what you do or imply. I just mean in general because that's the situation it would lead to if I were to raid on that day.)
But also beyond that, I don't think it's unusual at all that people just expect you to be present that day? It is a special family holiday after all. In my experience, even if you don't do big celebrations with your extended family many people just seem to appreciate to be in each other's company and not have everybody lock themselves away for hours of individual and isolated activities/screentime.
If I were to say "ok, have fun preparing everything, I'm gonna raid the whole day, call me when Christmas dinner is ready but leave me alone beyond that because I'd rather get that clear than spending time with you on this one important day" then in my individual case that would certainly be met with distcontent.
(And personally I think that's fair because I do like to spend time with my family that day. We are quite relaxed so there is not much performative stuff to worry about. Outside of preparations for Christmas Eve we just sit together, talk, have walks, have coffee etc..)
I know, everybody celebrates Christmas differently and my observations are just anecdotal. But so are those of the people spending little time with their family over the course of the day except for presents/dinner.
It's all very individual so I don't think SE should expect that people (outside of Japan) can make room to raid on that day. Some will certainly be able to, but others will certainly be not.