Interesting question. Back in the 60's to 80's, if you bought a Tek scope, all the theory of operation, calibration, service info and schematics, were all provided, and since those guys really understood analogue design, and how to get the best from it, technical prowess of the highest border, it was easy to learn such techniques for other designs, by reading the manuals. Recently took the cover of the lab TDS2024B scope and that has iirc, about 3 large chips on the pcb, and that's about it. No schematics and none of the info that come with the older designs. Same with HP kit, from past to present.
Reason ?: Far east, in places, spends much their time reverse engineering and stealing ip of western kit, no R&D cost, so they can copy and sell at a fraction of the price. Don't work in that part of the industry, but would think that it's a real fight for survival for the hp and tek of this world now. Security by obscurity amy not be a long term solution, but it must help...