Why do people under rate Mariah Carey?

People always write her off like she is just some other artist like rihana or something but she like writes all of her songs she has sold like 200 million albums and she has 18 number ones all together she is the most successful female recording artist ever. Oh and plus people always diss the album glitter as if it was like a major flop but it actaully went platnum soo..... And the lead single loverboy was a hit and peaked at number 2 so if it wasnt for all the bull that was going on during 911 it would have went to number one! People say she cant sing anymore but i beg to differ if you look at her most recent christmas performances!!!!! So why doesnt everyone know about all this?????