Please remember you don't have to be American to understand American things. We have our own complex and bizarre food days, often celebrating a particular point of view of an event that might not have happened too you know :-D
Indeed a lot of Americans probably think Thanksgiving is a pain, or historically offensive or fun but not that big a deal.
Some people don't have families to celebrate with and it's depressing spending feast days on your own if you think feast days are important. I personally like to spend Christmas with my family because it's important to them and it's a good chance to see people I don't normally get a chance to but I'm not a child anymore and not a Christian so the actually day holds no value to me outside the value it has to others (does that makes sense?).
If I could work a day that allowed someone who cared passionately about the holiday to have the day off (and I got a bit more for it) I may come to the conclusion that the day itself isn't worth the sacrifice of the possibility of added money value for my hours of finite lifespan. These are the decisions adults have to make.
Other people may agree with the spirit of the holiday but not like their families or not have friends available so they might as well work even if it's just for the regular wage.
Being forced to work a holiday without compensation of any kind is horrible but I assume if the day was that important to you and your employer was so unreasonable you would look for work elsewhere.
Being forced not to work a holiday because the holiday is important to someone else is a bit daft though.