That's interesting because... "
Surgical stainless steel is a grade of
stainless steel used in biomedical applications. The most common "surgical steels" are
austenitic SAE 316 stainless and
martensitic SAE 440, SAE 420, and
17-4 stainless steels.
[1] There is no formal definition on what constitutes a "surgical stainless steel", so product manufacturers and distributors often apply the term to refer to any grade of corrosion resistant steel." - Wikipedia
en.wikipedia.org
I've worked with both aluminum and steel in the industrial sector and there is a huge difference in the quality of materials. But when it comes to phone durability try dropping a 13 or Mini from about 20 feet (or any Android Phone) and see how well that Aluminum protects the glass. It won't be able to withstand the impact.
Surgical steel is a combination of the 2 best stainless steels for corrosion resistance, that's the main reason, but if you want a quality product and a durable one you don't want aluminum. It bends very easily causing the glass to take more impact so companies like Samsung have to make up for that with a more durable glass.
Either way if you want a durable phone you are going to have to pay more for quality materials so that's a big thing. You could always get a bulky case for extra protection or screen protectors etc. I think despite the fact that raw materials are more expensive for aluminum, steel is always a better choice for durability. Steel is very easy to find and even though it's in high demand too aluminum has more of a supply / demand problem.
The reality is aluminum bends and melts very easily compared to steel, it has great uses for us but surgical steel with tempered glass is a great idea for a phone. A plastic or metal back might be a better idea TBH but I would definitely pay more for solid steel construction.