They produce less heat because they are an inferior versions of a standalone GPU. It's harder to extract heat from two chips in the same space (CPU and GPU) than two separate chips, also you're limited in chip space for transistor count. (I'm assuming inferior refers to compute performance and integrated means integrated on to the same chip btw., if that's not what you meant then ignore my comment).
> They produce less heat because they are an inferior versions of a standalone GPU.
Isn't that entirely based on what they integrate? The market has traditionally been such that integrated units are for cost, and so are paired with cheaper GPU components. I don't know of any technical reason that integrated units use low end GPU specs, just business reasons. Any normal market pressures would be different in this case, based on the size of the order and specific needs.
> I'm assuming inferior refers to compute performance
Inferior based on maximum possible compute performance, sure. The top of the line dedicated GPU will have more leeway to work with than the top of the line integrated, but we're hardly talking about top of the line, we're talking about matching three year old hardware.
It does because of thermals.