Symbolic math proofs are hard for most people to follow. This particularly applies if they are lost.
When they understand in words what the proposition being proved is, and understand in words the idea of the proof and better yet the steps themselves, then they can follow the symbols.
Because foundations of counting and addition lack materials explaining them in words, teachers are unable to learn and math ed college programs are unable to teach this material.
Thus the math behind elementary math and the math behind the Common Core Standards is not available to teachers or in math ed programs in college.