isn't this really developer dependent no matter the hardware?
We can get 60fps games right now.
To an extent, yeah.
The problem now is that, like Phil mentioned, there's a big gap between CPU and GPU. So if Devs want to make a game 60FPS they generally have to make a choice to not fully utilize the GPU. The industry still sells games largely off of screenshots and YouTube videos where graphics are far more apparent than framerate, so it's not a shock that most of them choose to utilize the GPU, at which point the CPU can't keep up.
In theory, if they were closer in power to each other, you could still utilize the GPU to it's capacity and the CPU would still be able to handle 60FPS (obviously mileage will vary depending on the type of game and the other stuff they might be doing with the CPU as a result, large open world games will inherently put a bigger strain on the CPU for example).
So ultimately you're right, it's a developers choice. But you make the choice a lot easier by allowing them to more or less do both at the same time.