Steel wheels are often used in Winter due to its low cost, however, it is very prone to rust. Why are Stainless Steel wheels, more specifically 316 Stainless Steel not being more popular as the material it is being use in marine environments where corrosion is even higher than salt in Winter?
I second Gabriel's comment: Probably cost. Nickel Moly Chromium Stainless (316) is very expensive, this random kitchen sink is just a sheet of stainless stamped into a cube, and it's $500+ retail. Given the price I have to assume it's 316, otherwise it would be even more.
I can only imagine what a single wheel would cost a manufacturer. Even using Powdered metal for casting is still expensive, from this place 45 micron 316 will run you $350 for 2kg, which is only about 4.5 lbs. Not sure how much you need to make a wheel, but you can see where I'm going. Even buying crazy amounts in bulk probably steel (!) wouldn't break the cost-benefit ratio (profit-trouble ratio?).
You may however take a page out of the exhaust manufacturer's book, and coat your wheels with aluminum some sort of way, maybe elctroplating or something. It may not be the most stylish (then again, maybe it might), but it would certainly be cost effective to go the diy route.
Disclosure: I'm not a metallurgist, but I have an intro to metallurgy class this semester, and we just talked about stainless steel the other day, so that and the fact I'm into cars peaked my interest in this question :-)
Largely because it's unnecessary. Steel wheels are so incredibly cheap compared to stainless that there's no benefit. Steel wheels are heavy enough that it takes way beyond the normal life of a car for them to rust out too (I have a 22 year old car that I drive in the winters on original steel wheels and the wheels are in better shape than the car body). It's also normal to use wheelcovers on steel wheels to hide the unsightly surface rust that does sometimes appear over the years.