Don't understand

I have spent a lot of time and money taking care of my brothers over the years.  Maybe not in the last 3 years, but up until then.  Every time one of them needed help in some way, they always called me.  They didn't ever call one of the other brothers, they always called me.  Keep in mind, I was the only sister in the family, not sure that was it or if they felt I was the only stable one.  I have/had 3 brothers, which I have help in one way or another, some several times.  Don't get me wrong, I love/loved my brothers, but they never showed me that they appreciated any of the help that was given to them.  I have NEVER received from any of them, a birthday card, a holiday card or anything to show that they love me and/or appreciated anything that I did for them.  I have never said anything to them, but I wish I would have maybe I wouldn't feel so alone when it comes to family since there is only 3 of the 4 of us around.  We lost our parents when we were all young. Our father died at the age of 43 and our mother died at the age of 46.  I miss them very much because they never really got to see any of us grow up to be adults and parents.  Not sure if our parents lived longer if my brothers would have been different.