This really surprises me, I didn't realise how different my family was and its not something I have ever questioned. If you don't have a bedroom for the child that is a different matter but in my family we have always had our own room and put to bed in our own room where we were expected to stay from being a toddler onwards. Bath, bedtime stories with lots of love and hugs (in our own bed, and then lights out - well depending on the age obviously.
This was how I, all my cousins and friends were brought up. The transition to our own bed was like potty training , it was an expectation and each child differed as to when they achieved it but as soon as they could they would be in their own room even from being a babe in arms - otherwise what do you do if you have multiple kids? Buy a super king size bed? What about intimacy with your partner?
Their bed, their bedroom is the default in my world. Co-sleeping is allowed/welcomed when they are ill or have had a bad dream. Or maybe something upsetting has happened.
As a child (before I could walk) I had my own room or shared a room (not a bed) with my sister. If say I woke up during the night, I would generally just roll over and go back to sleep. If I woke up and was scared/ upset due to a bad dream or I felt ill, I would get out of bed, bypass my sister who was in the same room and crawl in between my mum and dad. As a child I obviously had the ability to teleport myself back to my own bed😁, as I would frequently fall asleep cuddling one parent or another but still manage to wake up in my own bed.
As kids get older (late teens onwards) there maybe odd nights sharing for basically the same reasons or just for bonding, fun sharing time i.e. cosying up in bed etc whilst on holiday to watch a film or catch up. And then there have been cold nights, were we have cuddled up for warmth (Ok - get the violins out)!
Never realised this wasn't the norm.
So I totally get the OPs feelings but without mum being onboard, its a difficult one.