Who told you that? Maybe you should try firing up some thread monitors before you talk this bullshit. Most games of any complexity, and even many games of virtually none, are multithreaded. This was mostly true even before the advent of the Xbox 360, but after that just about every cross-platform game became multithreaded, with at least three threads. Since Microsoft and Sony have both gone to consoles with eight cores, multithreaded games are even more ubiquitous.
So no, you're full of crap right there.
Well there certainly are more threads in use, but the real question is what are they doing? The biggest bottleneck in games - as far as the CPU is concerned - is setting up your command lists and buffers. In current GPU APIs this is a sequential process and is inherently single-threaded. You can do multithreading to some degree (see DX11 multi-threading) but the actual access to the immediate context is single-threaded so you suffer the synchronization penalty anyway which is why DX11 single-threaded vs multi-threaded is such a mixed bag performance-wise.
DX12 and Vulkan aim to change that by reducing the responsibility of the driver and moving that responsibility to the application, this allows for a less sequential pipeline.
So you're somewhat right but the question isn't how many threads there are but what they are doing, also your suggestion of a thread monitor will often produce a bit of a red herring since it will also collect synchronization overhead. For example you can have it show one core maxed out and then 8 cores maxed out but the application doesn't run any faster, the reason is the same: the pipeline is inherently sequential so the usage you are seeing is just busy-wait, it's not actually doing anything though, sometimes this overhead is so large you see it actually making the multi-threaded version run slower.