In actuality, one might find "lol what if the characters were JEWISH!" funny if they had a lowly, juvenile and shitty sense of humor, which apparently you do. The "hey lets take a game / movie / TV show / vocation and replace the people who traditionally do those things with someone of a different ethnicity" style of joking is as fucking tired and clichè and "yo mama" and "knock knock" jokes. It's tantamount to saying "Heh heh... hey, guys, you know how the President is a man? Well, I bet if a WOMAN was president, she'd, like... totally declare war on people when she was on her period! Or like get makeup and flour all over the Oval Office!", or "White people drive like this, but Black people drive like this".
In other words, it would be funny if the same fucking joke hadn't already been told about a million times by Carlos Mencia alone. You probably find it funny because you're too busy being trapped in the 80's retro hair metal acid wash jeans slap braclet time warp that you live in.