My ex could be like this (he's not seen dd for several years) treating her much younger than she is and not letting her do stuff.
Dd is a very capable, sensible and independent sort and it drove her nuts!
This is a child who's been helping with housework including "proper" cooking (inc peeling and chopping) doing her own laundry etc since she was about 10/11 and at 13 almost 14 he was still trying to tell her what to wear, not letting her make hot drinks or get something out the oven... Even giving her far too small portions (basing it on eldest with wife 2's child who's years younger and not a big eater) and not letting her drink after a certain point in the evening!
The food and drink issues were particularly problematic as dd has a disability (which he knows! And has been told about these details) which mean she has a high metabolism and needs to adjust for that and also is prone to dehydration 😡 arse!
I don't know why.
I guess there's elements of not being used to that child, not progressing that child's age/development in their mind, not wanting them to "grow up too fast" but it's also not bloody listening, not tuning into the child's needs, not observing and making appropriate adjustments.
Maddening!
However I've also noticed it within other families where the nrp factor doesn't exist.
Dd is 18 now but she's got friends who STILL aren't allowed to use the kettle, frying pan because it wouldn't be safe 🙄
Certainly at 16 the number who were allowed to do very little because they weren't trusted to do certain things safely or to an appropriate standard was ridiculous!
I first noticed a very few cases when I was a scout leader, particularly on camp but it was rare and the other scouts also registered it as nonsense and encouraged these kids to have a go at peeling and chopping veg etc
I noticed it edging in as a more frequent/normal thing about 15 years ago when I was at uni as a mature student and a certain type of student (18, coming to uni straight from home, often but not always privately educated) who were utterly clueless on really basic tasks - budgeting, cooking really simple things like pasta or eggs, laundry (many mixed wash and shrinkage incidents because they didn't know to separate certain colours or how to read wash labels)...
Their parents had really let them down in my opinion by not preparing them, in some instances the lack of knowledge left them really stuck for money!
Infantilising our kids is not helpful to them.
"It does sound OP as if you are jealous of him paying his daughter attention." Rubbish! I'm hardly the great defender of step mums but even I think that's bonkers!