Kids are being taught those skills, but you have to start with a base of fundamentals before you can move on to advanced thinking. Literacy is the biggest struggle and goal of elementary years. We want literate students so they can access information that allows the to think critically and use facts to support their ideas.

Neuroplasticity is also not something we lose; it just changes in its purpose later in life. Our brain is constantly making changes and growing with us, for better or worse. What you are thinking of are critical periods of development, such as with language acquisition and vision. These are our permanent systems, so our brain has evolved to not make many changes to our "framework" so to speak after these critical periods. There is no critical period for objective reasoning and critical thinking.

I would also point out that our brains do not finish developing in our frontal cortex (all executive functioning, decision making, and risk evaluation) until our mid twenties.

We need kids that can read independently before they can truly think independently. Gotta walk before you run, and most of my students are still learning to walk.

Source: I teach 6th grade science and my degrees are in neuroscience and education.