The corrosion factor is just a small reason. The MAIN reason is strength.
Stainless bolts are WAYYYY weaker than a grade 8 bolt. This is because stainless can not be hardened due to low carbon content. Never use stainless fasteners for something your life may depend on.
Can i clarify? Stainless is weak in that it is so hard due to the chromium content that it is brittle. The same is true for high carbon steel. It is so hard that it is brittle. It is still technically strong but in shear or in tension it will have a tendency to break instead of stretch. This is why there are so many types of steel, for different applications. but in drive train and other critical parts you want the steel so stretch and 'deform' a little before it will break. regular carbon steel (like grade 8 bolts) will actually harden as well when they stretch, increasing their strength. This can be a good thing if stretching is done properly (pre-stretched bolts are used in applications like brake calipers to a) strengthen them and b) limit the amount they stretch when you tighten them so they don't have as much tendency to try to come loose.) However its a fairly precise process and if stretched too far the bolts become weak and or brittle and can break