Modding the game is performed by going into the fundamental scripts and altering the code, or learning the code at its core. It isn't a stretch of the imagination to suggest learning and being able to manipulate the underlying game code is where all botting, hacking, duping, and other exploits come from. While modding is a nice refreshing take on a classic game, the real methods of modding are used to turn diablo 2 into an online money market exploit economy, a depressing hoarding and shopaholic orgy, and ultimately a barren wasteland of brain dead addicts who don't care about the game at all. Being able to alter or learn the fundamental code of the game is where cheating comes from.

No modding happened because people want to play the game not bot it
People made bots to make a profit you are correct on that

How exactly is a game going to prevent me from accessing its physical memory and/or assembly instructions it needs to operate on that physical memory?

The answer to your thread is an objective no.