There is a high likelihood of the adult adoptees engaging in these studies being ones whose lives are all about adoption. The happy well rounded ones are probably not engaging in discussing their adoption years later.
I know a fair bit professionally about adoption and trauma.
I think for over 5s that have been removed but maybe don't have frightening memories, there might be some argument for contact. Those people have been parents to that child, even if not excellent ones.
Those removed as babies and young children, I really struggle to understand why you would want to be nipping off for a cosy day at the zoo with them.
I'm really alarmed by it and I worry that once it becomes a thing, birth families will be coming forward making requests to see children long since adopted, putting their parents in a difficult position.
They had the children removed for a reason. They aren't just being looked after somewhere else, by some kindly folk, for them to visit.
I do however agree that letter writing is odd in 2025 and think that a better idea would be a message board app like the schools and nurseries use, where you could post little updates (& photos if you do that) for them to comment on on specific dates (I.e. not free flowing contact necessarily but on the month the letter would be due).
I think a lot more birth parents would log on and respond if you put a little social media style update of "Thor learnt to ride his bike last month & Jack got his 10 meter badge at swimming. We just came back off holiday" so they could just post a great news!
I don't think a lot of birth families have the literacy, organisation or sometimes motivation to write letters, especially when there are multiple kids in different families and they aren't a letter writing generation.