I think sleeping all night unaided is a developmental stage, not much different from walking and talking. It would be silly to get het up about a baby not walking by 8 months, or to congratulate yourself for excellent parenting if your baby walks at 10 months, because we get that babies walk when they're ready to do so. I think sleeping is similar and that it is perfectly normal for children to take a few years to reach readiness for this.
I had a bit of a paradigm shift when DD, who was bf / rocked / cuddled to sleep until toddlerhood and who had free access to our bed, chose to decamp to her own bed aged 3, shortly after DS was born. She just did it, and ever since then has slept beautifully.
DS has just started choosing his own bed now, aged 5. It's a gradual process and is entirely his choice - he goes in his bed for a few nights, then comes back to mine, I don't express an opinion either way. Very similar actually to how he stopped bf - he decided he didn't need it any more for a couple of days, then came back to it, then stopped entirely (this was aged 4). I think that if there had been a younger sibling, he'd have decamped sooner, like DD.
I suspect there is a spectrum - some children will be ready and willing to sleep all night unaided by an early age (and I think 8 months is very early), and some will need much longer. Of those who need longer, some can be pushed or encouraged via sleep-training techniques, and some cannot. Personality and emotional needs play a part here.
I think MN presents quite a variety of viewpoints on infant sleeping, and this is a GOOD thing. I, for one, would have appreciated someone to tell me that DD at 6 months was still tiny, did not need to be "sleeping through" and that her need for me was normal, healthy and valid and would remain so for years to come. The prevailing dogma of "babies must sleep through by 6 months and if not here's what you must do to make them!!" is unhelpful if unchallenged, and I'm extremely glad I did not go down any sleep-training route. The DCs are fine and secure and happy, they spent zero time sobbing in cots, I had very little sleep deprivation after the newborn days and we all loved sleeping together. It worked for us.