The family we are born into, why is it so, is it karma? I think not.
There are all sorts of theories about this matter, I think it is just an accident of birth, if we are lucky we get a really good one, most -people get an okay one, some get absolute shockers.
Children are extremely clever at working out how best to survive the family they are born into, the unfair thing is the very skills they learn or adapt to to survive their birth family is what keeps them stuck as adults.
If your survival strategy was to keep out of the way, you might be a person who tends to isolate.
If it was clear that being assertive would end up with you or someone else being harmed, you learn not to be assertive, thus making it very difficult to be assertive as an adult.
There are many variations on this theme, that is why it is so helpful to understand why you do what you do, so you can change it if you wish, it is not about blame, it is about self discovery and self realization.