Chemically fat and water are much different. Fat is an organic with very little polarity. Water is a non-organic and very polar.
Polar means one side is positive and another side is negative. In water the oxygen is dominate and pulls in extra negative charge.
Most spice (if not all depending on your definition) is organic. Spice will concentrate in fat. If you don't have enough fat the spice will just fall out of solution and be a solid at the bottom of the pot.
Salt dissociates into positive and negative ions is soluble in water as what happens is negative oxygen in the water hugs the positive (NA) and the hydrogen hugs the negative (CL). Again if you don't have enough water (huggers) the salt will just fall out as a solid.
I know a strange analogy. Alcohol is out of your system in 24-48 hours as it is not fat soluble. Marijuana is organic (spice like) and is fat soluble. It can be detected up to 30 days.