Probably because when it comes to religions, Judaism is somehow the least offensive.

I mean, when you look at Hanukkah specials, even kids specials, they always discuss the religious aspect of the holiday, yet, on the same token, if you try to discuss the religious aspect of Christmas, it's "offensive"... I was surprised that nobody complained about SESAME STREET had a nativity pageant for a holiday special over ten years ago. Other than that, A JOHNNY BRAVO CHRISTMAS briefly mentioned that Christmas is the birth of Baby Jesus, that much I can remember.

But again, I think it's mostly because Judaism is somehow the least offensive religion there is, maybe because there are so many Jews in entertainment business? I don't know... I always found it interesting with so many Jewish writers and producers out there, that if they write religious characters, they write them as Roman Catholic, but I digress.

Another theory is that Christianity is perhaps the most common practiced religion among Americans, so they're probably wanting to teach more about Judaism and bring more attention to it, because let's face it, when it comes to all the major holidays, the likes of Passover, Hanukkah, Yom Kippur are always overshadowed by Easter, Christmas, Thanksgiving, etc...

I thought I read somewhere that Marc Brown was Jewish himself. That may be completely false (please correct me if I'm wrong), but it could be partly why Judaism is focused on the most throughout the show.

Marc Brown is in fact Jewish according to the Elwood City Downtown Core: http://www.angelfire.com/ma2/ecdc/arthursperfectchristmas/apc201.htm

One thing that I like about Arthur is that the producers are not afraid to step into any issue that they feel like covering. Most other children's shows would never even dream about going into topics covered on "The Great MacGrady," "Arthur's Big Hit," and many others. Many other networks have strict guidelines on what can and can't be said on their airwaves. I know for a fact that Nickelodeon had a no religion policy unless it's part of a holiday special. An example that I know of is in an early draft of a Rugrats script. It had a quick religious line it, but Nick demanded that the line be removed. I'm not sure if they are still this strict, but this was back in the late 90s.

On a side note, did you know that Judaism is not shown in children's TV very much? One of the reasons that the religious line example from Rugrats stayed in my memory was because it had a lot of other Jewish references in it. Apparently this was notable for the time, or at least enough to warrant its own Wikipedia page: http://en.wikipedia.org/wiki/Judaism_in_Rugrats