In recent years there has been a trend shift away from this, at least in the AAA engines, towards a job system. This makes sense: you have a thread per core and you create jobs to “go wide” when you can. See for example Unity’s Job system it’s the GDC talk by Naughty Dog from a few years ago.
The big games will also prepare data for rendering in parallel (eg culling and sorting and whatnot, although much if this is also done on the GPU).
(Going by GDC talks, the rendering teardown articles and just what I see online from Unity/Unreal. I don’t work in games myself)
Which makes total sense because single thread performance is growing more slowly these days. Used to be you'd double every couple of years but today the midrange is only about 50% faster single threaded than it was in '16. Now if you count all the cores you're still seeing things more than double over that time. Compare these similarly priced CPUs from today and a few years ago: i5-6500 and i5-10500. The latter is maybe 30-40% faster single threaded but has more than double the parallel throughput.
I don't know why AI shouldn't thread well, assuming there is more than one actor. As long as they are operating over an immutable view of the game state, each actor should be able to plan independently and enter its commands independently. Likewise, there are probably some tricks you can do with physics. And anyway in most games interactive physics is only done for a few objects in the game world, and those objects are often not interacting with each other, at least not physically. You could cluster the objects that can affect each other and then do each of them single-threaded.
> As long as they are operating over an immutable view of the game state
That's a big issue. There is a surprising amount of back and forth between objects in a single step of gameplay/AI.
And, generally gameplay code tends to be a big mess of wild and ever-changing requirements from gameplay designers, extreme time crunch and short term (1 game then burn it) goals. Ivory tower software architecture it is not...
Clustering physics into "islands" is common practice though.
I'm not a game dev but I do know how software can become a mess. I think engines that are used by many games have a chance to push good practices here.
The big games will also prepare data for rendering in parallel (eg culling and sorting and whatnot, although much if this is also done on the GPU).
(Going by GDC talks, the rendering teardown articles and just what I see online from Unity/Unreal. I don’t work in games myself)