Dr Sarah Buckley writes a lot about this (among others), and her take on it is (and I'm sorry to reduce it to this!) that it is to do with the interruption to the hormone transfer that labour initiates. The hormone process is gearing up to the establishment of breastfeeding and bonding, priming the body for the super boost of oxytocin that locks in bonding and intoxication with your baby.
That's not to say ALL c-sections will have a troubled breastfeeding establishment, just a very compelling number of them will and that makes it highly likely that breastfeeding won't be a seamless affair with medical intervention.
What it does mean is that, knowing this, it gives mums the heads up as to how much harder they're looking at working on breastfeeding establishment if, for whatever reason, they end up with interventions that hijack the hormone production. There is the increasing practice of skin-to-skin as soon as possible after the baby is lifted out, minimal handling by staff, expert lactation consultants on hand etc. by more and more obs and hospitals. It's still not optimal, it does optimise the chances of the body playing catch-ups with the hormone production.
So many women get jibbed when their care givers are 'informing' them about c-sections, inductions, epidurals etc and don't consider breastfeeding implications important enough to share with their clients. The clients, then, assume that breastfeeding can just start and they are the ones who are highly likely to be on formula within 4 weeks because the whole system that's supposed to be supporting them fails them, yet pats itself on the back for a 'good outcome' - while the mothers lament and wonder what went wrong
Birth method and experience has been shown and is continuing to predict breastfeeding establishment and retention - it seems every issue of Essence (ABA's mag) as well as articles in nursing journals contains at least one report supporting this.
It's time to for the medical fraternity to stop kidding themselves and inadvertently cheating women by trotting out the tired "at least you got a healthy baby", because 'health' is more than just AGPAR scores and the time till discharge, or even the first 6 weeks, or even the first 6 months. Many would argue that effects into adulthood mean that the birth was not a 'good outcome'.
Anecdotallly - my MiL had two inductions for my DP and ended up with an emergency c-section. She breastfed for barely 3 months and had problems. She had an elective c-section with BiL and was able to have him within 3 hours (it was 3 days with DP) and to hold him to get things started and she BF him for 6 months. The effects in their attachment (to others close to them) can still be seen. DP was definitely disadvantaged from his forced separation at birth, and many important neural connections were never made with DP - he has a condition related to dyslexia and his empathy skills are almost non-existent, where his brother is someone who 'feels' and he is immediately a very warm person. Back in the bad old 70s women had even less idea about how to optimise bonding and no-one in hospitals bothered themselves with getting mothers and babies together for breastfeeding and bonding
Anecdote is not evidence, and there is plenty of evidence, and a growing body of longitudinal study.
Just this year, whilst studying schizophrenia for uni, there was a definite correlation between birth experience/type and the predisposition to schizophrenia. That scared the hell out of me, because NO-ONE talks about this in birthing/obstetric circles, they only seem to talk about it in hindsight in terms of etiology of schizophrenia and some other mental illnesses. To me that is unforgiveable - these findings need to be shared so that compensations for unavoidable (hell, even elective) birth interventions can be implemented as soon as humanly and medically possible.
Already, the body of evidence for the immense benefits of kangaroo care is massive - yet it's only really used in practice for premmies, and only sometimes (if you're lucky enough to be in a hospital that is savvy enough), where it really needs to be a policy for all c-sections and all babies going into NICU/SCN.
I'm getting ahead of myself, here