Should I be upset with my sister? I'm a realtor and my sister & her husband are buying their 5th home?

I am a full time agent, work strictly on commission, my sister & husband are purchasing their 5th home (this time a million dollar home) and again they are not using my services. Her argument is she is not the breadwinner and therefore does not have much sayso in the matter of agency. however I know she is the driving force and brains of there marriage, and she knows I know this. So that argument is frivolous. I am just bewildered at this point, how can your one and only sister not help the other out. If the situation was reversed I would use her in a heartbeat or do anything to make her life better if it was within my power. My husband family would not think twice of using another realtor, and these are my inlaws. Who would ever think they would think more of me than my own sister. Please help me understand this.