Not all schools are the same, so I don't who the "they" are that you are referring to.
I don't see anyone "slacking off teaching educational materials."
On the contrary.
I see 4-5 yr. olds expected to know material that used to be reserved for 7 yr. olds.
I see the classroom setting and curriculum designed for the strengths of young girls to the detriment of young boys.
One year of maturity at this young age makes a huge difference, and today's kids are being denied that.
I can only express my own views of teaching 4 and 5 year old kids what we used to teach 6 an 7 year old children. I do not think that is wise on our part. Some people see it as giving a head start and I see it as pushing these kids into a structured process 1/3rd of their lifespans earlier.
Two years is a very long time in the life of a four year old child. What seems like an hour to us, at that age seems like a week. What seems like a year to us seems like a decade to them.
My aunt was the education secretary for a parochial school network in Texas. She taught in the class room for many years. In her opinion young boys especially, were not geared to be trapped inside a school until seven. Her observation was that they might start a little later, but they caught up quickly, when allowed to be a child first, then go to school when they were ready.
I cannot help but think we are seriously screwing up the growing process of these children.