Question Why do people directly connect CPU and GPU water blocks together?

Dec 2, 2020
I've had this question for quite a long time. Why do most people connect CPU block directly to GPU blocks without radiators in between while building their water cooling system? It's also very common in manufacturers' example cooling systems. The coolant is heated by CPU block and then flows to GPU block without being cooled, and this is not good for cooling the GPU, isn't it?

For example, I have two water cooling systems for gaming PCs, both using the same cases and 360 radiators:
  1. CPU block → GPU block → Radiator 1 → Radiator 2 → Distro Plate (with pump)
  2. CPU block → Radiator 1 → GPU block → Radiator 2 → Distro Plate (with pump)
Do these two systems have same or very different thermal efficiency? If it's same or close, what is the reason? I personally prefer the second one, by the way.
From what I have seen in reviews is the water temperature normalises after a bit of time and runs the same temperature all way around. This is why they say it doesn’t matter if the radiator is before/between/after the cpu & gpu. I have never done a custom loop but read/watched a few reviews on it over the years. This was something I wondered at one time but apparently it makes no difference.