Why is Mac cosmetics so expensive?!?

Hey everyone I was at Mac cosmetics not to long ago and I was looking at their lipglassess and they were like 20.00$ usually mine cost about 5 the lady said they were good quality but us there something else that makes it great? I can affored it but still it's crazy! MAC LIPGLASS: 20.00 JESSIES GIRL LIPGLASS 4.00