I mean, everything you want to learn about crypto is available online, in libraries, in textbooks. Including differential cryptoanalysis, the theory behind these mathematical forms (Galois Field makes things _EASIER_, not harder actually. That's why CRC-checks and Reed-Solomon codes were based off of Galois Fields, and AES being based on GF(2^8) is to take advantage of those same properties).
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What has happened is that the "old generation" of programmers is dying out / retiring. And they aren't passing on their knowledge to the new generation. The "old generation" of programmers were high-math, abstract algebra and more, while "new generation" programmers just never bothered to learn this stuff.