This is cool to look at but its worthless to use to learn Morse code. Actually learning requires recognizing audio patterns not quickly translating characters into words from a flowchart.
I think the charts were meant for an inexperienced or almost untrained operator (civilian in wartime e.g.) that could write down what they heard, then use a chart to decode it and maybe even send a reply.
It's effectively a Huffman tree based off the frequency letters occur in the English language used to minimize the overall symbol length duration of each letter in a message.