I have to imagine that the number of people who won't attend a game on Thanksgiving or Christmas dwarfs the number of people that won't show on Rosh Hashanah... I mean really? Are there going to be empty seats in the home opener of the Super Bowl champs because Baltimore Jews aren't showing up? That just doesn't seem likely to me.
Thanksgiving isn't a religious holiday (in fact, for many people, their Thanksgiving tradition is football). Christmas is closer, but most people don't consider Christmas to be a day of religious worship either. Easter would be a better example if one wants to at least start with an appropriate analogy.
Anyway, leaving aside issues of whether or not it's tradition, how about just understanding your customers? The city of Baltimore, without a doubt, wants the opportunity to defend their championship starting at home with the first game of the year. The Orioles either don't understand that or, more likely, simply don't care. I would argue that the majority of Orioles fans are Ravens fans who would want the game moved. I would also argue that quite a few Ravens fans are not Orioles fans partly because the owners keep doing shit like this.