Is there anything wrong with Michael Kors?

my mom is THAT gurl - she's elegant on a budget & i noticed she gravitated towards MK and Kate Spade, but not Coach. YSL is the only luxury brand bag she thinks makes cute bags too. im curious about the real differences between MK and Coach and why Coach seems to be more popular and well-liked. i personally like both brands, but why is MK viewed as a cheaper brand? is it quality / longevity? or something wrong with the brand?