Google search isn't a good example. AAA games are a great example when you think about graphics. However, most of that is trivially parallelizable, thus "all you need to do" is assign vertices/pixels to different threads (in quotation marks as that's of course not trivial by itself, but a different kind of engineering problem).

However, once you get into simulations you have billions (or multiple orders of magnitude more) elements interacting with each other. When you simulate a wave every element depends on it's neighbors and the finer the granularity the more accurate your simulation (in theory at least).

Thinking of graphics, though, i would assume most of that is in the GPU side. Simulations do make sense, but I see games like Factorio still focused on single thread first. And then look for natural parallel segments.

That is all to say that millions of events still feels like a lot. I am not shocked to know it can and does happen.

There are no good solutions for something like factorio. There are solutions that work but they aren't worth the trouble. My personal recommendation is that you split the world into independent chunks. A big interconnected factorio map is a nightmare scenario because there is hardly anywhere where you can neatly split things up. Just one conveyor belt and you lose. Aka parallelize disconnected subgraphs.

So the game would have to be programmed so that conveyor belts and train tracks can be placed at region boundaries and that there is a hidden buffer to teleport things between regions. Now you need an algorithm to divide your graph to both minimize the imbalance between the number of nodes in the subgraph but also to minimize the edges between subgraphs.

Just dreaming over here, but if someone had the opportunity to rebuild a Factorio from the ground up, I bet they could design something massively scalable. Something based in cell automata, like how water flow works in Minecraft. Current cell state = f(prev cell state, neighboring cell states).

It would take some careful work to ensure that items didn't get duplicated or lost at junctions, and a back-pressure system for conveyor belt queues. Electrical signals would be transmitted at some speed limit.