Electronics distributors have published educational material for decades. Knowing how something works and how to choose the best option reduces their support burden and itself a form of marketing.

Omega Engineering used to (still does?) publish a set of absolutely massive hardcover catalogs on sensors and industrial controls that contained detailed tutorials and theory of operation. In some cases, they published entire books devoted to teaching you how stuff worked. Their Temperature Sensors Handbook always had a place on my bookshelf for many years.