I think it’s because we are designed with a somewhat blank idea of what love is. We are born with a system that will become love, but we are born with it undefined. It’s similar to how we are born with a need for food, but not our culinary culture. It is during our formative years that we learn what love is just like we learn what delicious food is. Btw, in Spanish, when a kid doesn’t like to eat a specific food, it’s said that they haven’t learned to eat it yet. Back to the topic, the part that does come predefined is that we are to attach to our caregivers. Thus, we don’t leave them because we are designed to not leave them and have them teach us love.

Another issue is that as children, we don’t know we are being abused. What we’ve experienced in our families is all we know. From the perspective at this age, that’s just how life is. There’s no reason to leave.

Once we start realizing that not everyone goes through our experiences and that there are much nicer ways of relating to family, we can start recognizing that our familial situation is terrible and we want it to be different. The issue here is that there are only two options. Either you suffer the bad parts of the abuse while surviving on the breadcrumbs, or you lose any possibility of ever having a childhood family. The person basically has to decide to lose a major part of life. That is an immense amount of grief to endure, and they have to do it without the support of family. In these situations, the victim usually just kind of learns to manage the relationship unless there is a major catastrophic event that forces a decision. Otherwise, they’re learning how to overcome the frequent but comparatively tolerable difficulties. You’ll hear them say things like, “My dad is cool as long as you don’t expect him to…” or, “I love my mom, but I know not to…” They’re consolations to salvage their one opportunity. The decision is then to either (a) take a humongous hit by losing childhood family or (b) learn to deal with the most recent difficulty. The latter is much easier to brunt.

tl;dr: We don’t know it’s abuse. Instead, we are taught abuse is love. We are designed by birth to attach to our parents. And once we figure out it’s abuse, it’s a terribly difficult lose-lose decision to make where one option is addressing a recent issue and the other is nuclear.