Otherwise why aren’t all babies given up for adoption at birth?
There are many other options between intense automatic biologically-driven love described in the OP and wanting to adopt a child out (and wanting to do so can be driven by love, it's pretty nasty to think a birth mother making that choice musn't love her child enough).
The whole concept of instant-mother love is pretty modern and cultural specific - not everywhere makes that assumption. For some, kids are expected to be a burden that will hopefully be worthwhile, pregnancy a risk, and you do your best as a responsible adult no matter how you feel about it.
Even in this culture, many parents view their children as their responsibility even if they don't get the stereotypical rush of intense love. It's a common remark to those who don't that the love will grow. Sometimes this happens, sometimes it'll be a caring love but not one that fits the media image (I think this is the most common), and sometimes it never happens at all. The latter is more common if the child wasn't wanted by the mother in the first place - none of those steps are automatically going to change that.
In most places, in a married couple, one parent cannot give a child up for adoption without the consent of the other and in many communities it is socially unacceptable to adopt a child out (it's noticeable in some places how married women have a higher rate of abortion). The child is viewed as a social commodity and it is viewed as a failure particularly on the mother if even mentions she wants that option. There becomes more pressure in communities where it is assumed kids will provide long-term care and a woman's worth is connected to her ability to care for kids and pass on community traditions.
Mothers are generally viewed as monsters if we say we don't intensely love our kids more than anything from birth. Look at the recent 'do you love your OH or kids more' thread. If I say my spouse came more naturally to parenting, that he's more maternal than I will ever be, it's assumed something is wrong with me or that I must hate my kids. I don't, he just enjoys parenting more than I do, even when he was a SAHP.
Sure, those mothers who turn murderous are in the minority, but it wasn't something corrupt in their biology that made them that way anymore than any other animal mother who tries to kill her young, it wasn't that they didn't all and more than the OP's list, it wasn't that evolution failed in all of them (like evolution has some sort of plan here). Far more factors are involved in it. I don't think insta-love should be considered the standard for most mother's to live up to or that a cherrypicked view of biology should be viewed separate from the many environmental factors.