I get it. I used to beat myself up for it. Still do sometimes. But I have to remind myself that if they aren't reaching out either, they may feel the same. We both care about each other and if one or the other of us called we'd help in a heart beat or have a lengthy enjoyable conversation. But we also have lives to go about. And if they aren't involved in the day to day it takes concerted effort to reach out.
When I feel really bad is when I don't send a Xmas card but get one from them. Lol