How can some people just be dedicated to one brand of makeup ( brand loyal)?

It has a lot to do with the customer service, the advertisment, the price and the hype around MAC. When you buy some MAC products you're not paying a lot more than the most expensive drugstore product and getting high end (ie lipsticks). Some people just want to wear high end don't ask me why. I love a few MAC products but I agree with you on the eyeliner not so much on the primer though (Love Too Faced Shadow Insurance and MakeUp Forever's face primer (It's a matter of opinion though lol).