The models aren't particularly hard to implement, so a person who has spent his life and is one of the best game engine programmers in the world I don't think it would take that long to implement the cutting edge of todays machine learning models. Compared to game graphics shaders and the complex interactions you have to work with to get those performant and work correctly and display all the gameplay that happens the technical parts of machine learning are very simple.
I've worked building low level machine learning stuff at Google, it isn't that hard to do at all. The hard part is improving these models, not building them when you already know what to build.
> The hard part is ... not building them when you already know what to build.
Indeed. A somewhat sharp schoolchild could build a light bulb or an electric motor/generator, and understand the basic underlying principles, in a pretty short time. But how many decades did it take the first researchers and inventors of those things to get to that same point?
Heck, there was a high school kid who built a primitive semiconductor fab in their garage.[0]
But for novel advancements, even getting to the point where you have an idea of what isn't impossible is half the battle.
I've worked building low level machine learning stuff at Google, it isn't that hard to do at all. The hard part is improving these models, not building them when you already know what to build.