Eyebrows may have a practical function (avoiding sweat dripping into the eyes) but I suspect the main evolutionary pressure is through mate selection. People with eyebrows halfway up their forehead or below their eyes were sufficiently unattractive that those combinations of genes didn't propagate.

Since hair for the whole body is presumably encoded by some very non-modular genes, hair distribution on parts that aren't important for function or appearance may just be side-effects of changes that affected parts that are important.

Our species lost most of its body hair fairly recently, so the evolution of hair patterns is relatively incomplete.

Our eyebrow region is exceedingly expressive in terms of movement, similar to our mouth when not speaking (think of all the variations of smiles, frowns, smirks, etc.). The bands of hair make it much easier to identify that movement, especially from a few meters away. Eyebrows are for direct emotional signaling.

What we find attractive is also genetically determined, though. If very fit (in an evolutionary sense) people started to develop eyebrows half way up their face, that would quickly lead to a population of people who found that hot.

We don't have those types of glands on the backs of our knees or inner side of elbow, etc. So no extra hair there, and no need for antiperspirant there either.

However, it strikes me as more likely that pheromones are emitted in places already adapted for evaporative cooling, which in turn would be hairy places, which in turn could be lubricative.

You might be reversing cause and effect.

Better alternatives for so many functions that were never explored/reached by evolution.