"How come in the past - pupils could do a few practise papers and pass, what changed?"
Grade inflation, and rampant 'nuclear escalation' in tutoring.
Eg: 5 children - all equally clever and enthusiastic about learning
little Maria is bright and enjoys school. She is in a class of 30 at a well run state primary. There are 2 children with ADHD in her class who with no specific support, and her teacher is fairly newly qualified. Maria doesn't get a lot of her teacher's time, but her mum reads with her every week and helps her with her homework. Her mothers friend has told her to enter Maria for the 11+ and her mother intends to do so and assumes she will do fine.
Ann is as clever as Maria and is at the same state school and in the same class. However, her mother sits down with her every day and does maths practice for 20 minutes, followed by 20 minutes of writing. She also goes to a Saturday 11+ small group session for 3 hours, where she does small group, 11+ focused learning.
Fred is as clever as Ann, but he goes to a private prep school where he is one of only 13 children in class. He gets a lot of time with his teacher, who is an experienced maths specialist. He will be sitting the 11+. His parents won't do any special preparation because they assume they don't need to as Fred is near the top of his private school class in primary.
Marcus is in the same class as Fred and is also on the top table. His mother is more anxious about the 11+. and as a teacher herself has been working with him for an hour every night on 11+ type questions for the last 8 weeks running up to the exam. He also attended an 11+ summer camp and does 11+ booster sessions organised by his prep school.
Orla is in the same class as Fred and Marcus. Also on the top table. She's done everything that Fred and Marcus have done. She has also got an 11+ tutor who she's been seeing weekly for the past 6 months. Her parents are paying £60 per session for the tutor whose name she won't tell anyone. The tutor has got a 100% success record in getting children into superselectives so Orla's mother has high hopes for her.
Get it?
There is massive grade inflation and rampant tutoring. 1 in 3 in London and Kent. In my peer group I'd say it's more like two thirds of all children are tutored at some point.