Space near Earth is hot (apparently, ~ 120°C) in the sun, and cold in the shade (e.g., the Earth's shadow). On average, it's not particularly cold. You can get colder average temperatures on Earth, without the wide swings.
But more importantly, space is empty, and the best way to cool is to dump heat in some medium which carries it away (air is the basic one on Earth, but applications that really need cooling like to use water as a primary medium.) In space you've got...nothing, basically, somyou are stuck with radiating, which works, but poorly.
But more importantly, space is empty, and the best way to cool is to dump heat in some medium which carries it away (air is the basic one on Earth, but applications that really need cooling like to use water as a primary medium.) In space you've got...nothing, basically, somyou are stuck with radiating, which works, but poorly.