How many of the stars are vegans because its trendy in Hollywood to say you are vegan. Then when they get home their personal chef cooks them up a nice rack-o-lamb.
Some. For example Scarlett Johansson. In an interview she said when she gave up being a vegan/vegetarian and chomped down on a burger after a long long time, the feeling was akin to an orgasm ! Scarlett Johansson has a reputation in Hollywood of being a voracious meat eater, mostly off the dinner table.
However Jennifer Connelly is an ethical vegan and has been one for a long long time. So is Natalie Portman.
It's not just the meat, it shunning dairy and eggs as well. So, no baked goods w/eggs, no yogurt, no milk, no dairy-based ice cream, no cheese on your tofuburger. Most people don't want to limit their diet that much.
I know someone who professes to be vegan, but eats desserts w/o worrying about what's in them. As she says, "It's not a religion," but to many it is. They don't eat much that they haven't prepared themselves, much like someone who keeps kosher or halal.
There was some research that veganism was good for diabetics, so, being semi-veg myself, I thought I'd give it a spin, but sorry, I like yogurt and lord knows I like ice cream. As long as one picks lower fat versions (assuming health rather than politics is the reason for the diet), I don't see where a little dairy hurts you. And for someone watching carbs, eggs and egg products are great choices to help control blood sugar.
If folks would just go vegan w/o the politics, I wouldn't care, but it's the anti-corporate, anti-capitalist crap that comes with it that drives me nuts. Just don't eat the damn meat!