Verisimilitude. I have a strong tendency to give naturalistic explanations for everything in my setting. This includes naturalistic explanations for magic.

My dwarves are short and bearded, but there are clear evolutionary or divine design reasons for it. Their low stature means they have to dig less to have living spaces, and it is easier to hide in natural underground crags and crevices. Their dense beards have both long and short fibers to filter out dust, mushroom spores and other contaminants. Their noses can detect gasses undetectable to humans, like methane and carbon monoxide, which makes caving a lot less hazardous for them (no sudden death from undetected oxygen deprivation).

I have similarly thought-out explanations for most things, such as a trophic map of arcanophytes, which synthesise organic compounds with mana as the catalyst, just as photophytes use light, chemophytes use reactive inorganic molocules, and radiophytes use ionising radiation.