The thing is, I do not believe that sleeping through is better. I can completely understand it may be better for parents, especially if the parents don't want to co-sleep, or are bottle feeding, or the baby's night wakings are long and complicated, or the parents can't catch up on sleep in the day or any number of other reasons. I can absolutely see that, and if that's the case then it makes sense to try and achieve it. I don't believe it's harmful for a baby to sleep through either. I just don't believe that it's better. I don't think they need to sleep through to have "good sleep" from their perspective. I think it's unhelpful to present the belief "It's better for babies to sleep through" because it leads parents to think that they should be changing their baby's sleep patterns, which might be causing them no (or minimal) problems. I also have problems with adding judgement to babies' sleep in terms of them being good/bad sleepers, because again, it makes parents feel responsible for how "well" their baby sleeps and like it is something they are doing well or badly at. (I also have the same issue about food, but that's a whole other thread.)
That's why some of us get irritated about advice being thrown about to get babies into routines, or encourage self settling, or sleeping through from a young age. Not because we are unhappy about our own babies' sleep
- more that I hate seeing new mums in a flap because "the baby won't sleep alone" but they don't want to put in loads of effort into changing it now (because they are tired) or they don't want to leave the baby to cry (which is reasonable). Or feeling like they are doing something wrong if they hold their baby for naps, which is one of the loveliest things ever. (And can also make you feel trapped, in which case that's different.) The reality is you can do all of these things for as long as it is working for you and change them when it becomes an issue (unless you have one of a small number of babies who is resistant to sleep training - then you are just stuck with it unfortunately, but guilt that you "caused it" is neither helpful or likely to be true). No it won't happen overnight, so if you have a return to work or study or whatever else planned and know you'll need better sleep patterns it makes sense to start working on a plan 2-3 months in advance, but I hate the narrative that if you've not got them in a routine by say six weeks then their sleep at say a year is doomed - this is just nonsense.
Obviously, it's foolish to be completely baby led for months and then suddenly expect things to change overnight with no effort at all but I've never actually met any proponent of attachment parenting (even if just for newborns) who believes or says that. It's clear that these changes happen gradually. However perhaps we do need to be more honest with new parents about when they are likely to happen, because I think maybe we do them a disservice by being reluctant to explain to the exhausted mother of a six week old just how long the "normal" broken sleeping will last. Because I think most assume that it will get better by itself, if not by 6 months, certainly by 12 (which covers the period of most people's return to work in the UK), and if you are completely baby led both of these milestones are unlikely - anecdotally, 24 months seems to be about the average. However, by 6 or definitely 12, if you're looking to make small changes, the older a baby is the more receptive they are likely to be to those changes, so there can be a benefit in putting off a routine, or independent sleep steps, until they are older. And as I said earlier, I do think (again, anecdotally) that for formula/bottle fed or breastfed-in-a-bottle-like-pattern babies they do tend to get there gradually on their own that bit earlier too. And TBH, those babies are in a majority in the UK, so it starts to become a bit more clear as to why people might expect this kind of thing from all babies.