A game is more than just rendering, and modern games will absolutely get bottlenecked on lower-end CPUs well before you reach say 144 fps. GamersNexus has done a bunch of videos on the topic.
You are not wrong that there are many games that are bottle-necked on lower end CPUs.
I would argue that for many CPU bound games, they could find better ways to utilize the GPU for computation and it is likely they just didn't have the knowledge, time, or budget to do so.
It's easier to write CPU code, every programmer can do it, so it's the most often reached for tool.
Also, at high frame rates, the bottleneck is frequently the CPU due to it not feeding the GPU fast enough, so you lose frames. There is definitely a real world requirement of having a fast enough CPU to properly utilize a high end video card, even if it's just for shoving command buffers and nothing else.
