It's not at all a mystery. There are thousands of fragrance compounds, many of which react with the high pH of raw soap. But there are other characteristics too; ones that don't react might morph or fade or have odd usage limits (which are.ever-changing) or interact oddly with other scent compounds.
It's not simply a matter of avoiding a few chemicals, if it was, we'd have hundreds of perfectly behaved soaping fo's from every supplier.
Fragrance oil formulators balance all kinds of needs to create scents for use in soap or other products. It's a trade that takes a lot of training & time.
It's beyond the knowledge and testing ability of the homecrafter to create their own fragrance oils for soap, the materials costs would be insane. And the research would take years.
♡ You could learn to create your own perfume though as its requirements are far simpler and the amounts needed more affordable by humans.
If one is truly interested in learning about fragrance notes, they can peruse the aroma chemical offerings from sellers to the indie perfumery trade, and read and study the topic in books like those from Poucher or join online communities for perfumers like basenotes.
