When the people you refer to know there is no chance of them having their children back of course they would agree to adoption
No they wouldn't. With all respect, that isn't how people's minds work, least of all very dysunctional people, sometimes with mental health problems
I have three adopted children, I've heard scores more stories from adoptive parents i know, I've read dozens of information reports on waiting children, I've other child protection experience and I know approximate statistics for relinquished children versus adopted without consent children
Next to no parents ever agree to adoption, no matter how abusive they are or how incapable. They don't do it. Why would they consent to losing their children?
In ROI, where consent is usually manadatory, there are nearly 0 adoptions of abused children. It's a near enough flat 0, except a couple (single digits) granted by high courts. There are more than nearly 0 children every year who are raped, beaten, starved, neglected and harmed irreperably by abusive families