I mean, for every blue giant at say… 15,000K, how much empty space is there, and how much random gas, dust and other crap sitting out in that empty space at that 2.73K cosmic background radiation temp is there in the universe?
In other words, if out of the 7 billion people on earth, we had 100,000 who were somewhere above 5’9", but the other 6,999,900,000 were exactly 5’9" (69"), the average height is 69.00021429. If you round that to 2 decimal places, it’s still 69".
That’s my bet as to what’s going on in the universe- something similar to that.
Given, I am not a physicist and my knowledge is limited on this subject. Having said that, IIRC in the Brief history of time, there was mentioned the Cosmological principle which roughly as I understand states that the Universe looks homogeneous at the large scale. So the temperature averaged over volume or mass becomes a moot point.
Actually, it is a good point. Ignoring the dark matter for the moment, most protons and electrons in the Universe are either in stars or in nebulae, both of which are significantly warmer than the CMB. Those stars and nebulae are scattered basically uniformly across the Universe, on a large enough scale, but they’re still clustered into warm bits locally.