why do people seem to like people that are not so nice or too nice?

Im nice, kind, polite and agree with my friends and whatever or traspass to please people but people seen to avoid me but my sister is a sweetheart too but she is straightfoward, tells it like it is and says her own opinion. She disagrees with something she doesnt agree with and she has a lot of friends.
Some of my friends says she rather hang with my sister than me because I'm too nice and passive and boring.