The same goes for tablets.
Imagine the price of a tablet that could keep up with your desktop! I'm almost certain it doesn't even exist.

Business laptops usually have user-controllable fans and under light workloads these fans don't even need to run.
If you have a fancy slim laptop on the other hand that might be different because good cooling systems usually don't mix well with slim devices.

They produce the same amount of heat that goes in as electricity. So it's only a question of efficient components.

I own a 12" subnotebook for almost 8 years now. It weighs 2kg. Weight has never been an issue for me. Size on the other hand is.

True. But in this case the situation is not as bad as it might seem.
For myself and some friends I bought several laptops (Dell and Lenovo) from professional refurbishers during the last years. On all of them the Windows was optional.
All these devices were in excellent condition or any unforseen problems were easily resolved. I think this is a good alternative for anyone who doesn't need the latest hardware.

Then why would you buy a Chromebook?
I don't see how this situation differs from a Windows-bundled device.
The big disadvantage Chromebooks tend to have hardwarewise is their lack of mass storage. You can find similar "real laptops" that don't have this problem (if you care).

Does that matter? In my view the problem is not in the price but in the freedom of choice.
There's no logical reason why I should buy a device that's bundled with any OS.