Not absorbing water is actually a problem with using silicone fluid on a street vehicle. Because water will not mix with silicone fluid, when any moisture gets in the system it will form a tiny droplet. That droplet can move through the system. When it gets to the cylinder area, your brakes only have to get to just over 200 degrees for that droplet to boil which will cause vapor lock and loss of braking until it cools.
Glycol based fluids will absorb small amounts of moisture and disperse it through the system. Because the moisture is dissolved, small amounts will have much smaller effects on the boiling point. Wet reflux boiling point is the brake fluid specification which gives a measure of how badly the fluid will be affected by moisture. Brake fluids which are labelled LMA or LWS usually have an additive which reacts with the water so there's almost no change in the corrosion or boiling points.
