I think there are two truths to the matter, tbh.
In general, nursery staff are poorly paid on few hours. To break even, they have to max out ratios. If a child needs extra intervention, then they can do it in-house, or they can be involved in ratified processes. But to be involved in ratified processes means paperwork, meetings, expectations and benchmarking. So, they want to keep everything informal. No expectations=no failure/success=no demands=no extra work. Not because they aren't good, or caring, or helpful, but because they are overworked, underpaid, stressed and can't actually see a tangible benefit of all this 'work' for the result, which is likely to only be seen in years, not months.
Secondly, many many EY workers have done this job for years. They started working in EY settings when they were 'playschools', a nice quaint 'creche' run by parents to help out other mums. The job has changed immeasurably, and despite the alleged training, they really don't get much. Each setting only has to have 1 senco. So 1 person goes on a day course and 'feeds back' what they have gleamed to the other people. Hardly quality.
Additionally, you have to consider the stats. 2% of children nationally require and get statements. 2 in 100. Those children are not neatly distributed across the country, and many children have pervasive development disorders such as ASC/Aspergers/PDD-NOS. Lots of the children who are higher functioning actually do pretty well in MS preschools without support. They even do quite well with Year R. In Yr 1 the cracks start to really show. I know a girl who was dx with Aspergers at 8 years old - only flagged at 7, and yet, looking back, the signs were there, just subtle. I know another girl who was clearly ASD, with hearing loss and another medical condition, but is still being 'assessed' in Yr 1.
Now, if you imagine a setting like DD1's preschool, max. intake 24 per annum. In 4 years they might see 2 children with needs that warrant SA at some point in their education. DD1's preschool had never had a child with needs as significant as hers. But then, when you drill down into the statistics, only 0.4% of girls her age get a Special school placement. So, given the intake of DD1's preschool, assuming around 50% will be boys, and knowing that only around 12 will go to school each year, whilst the others won't go til the following year, it would take 8 years to see 100 girls through the end of preschool. On those stats, in 20 years there would be one child who goes to Special school.
We have in this forum, a skewed population. I only know of 6 children with SEN in RL. And that is a set of children ranging from 4-10. I only know 2 other children with SEN of DD1's age.