Why do Americans call aluminum aluminum?

Answer 1

Ahh the excitement of etymology!

When Humphrey Day originally in 1808named the metal he called it alumium.

He later (1812) changed this to aluminum.

Some British felt the name need to be spiffed up and made more "classical" sounding and proposed aluminium. This proposal was in keeping the traditional -ium ending on many other metals (potassium, sodium, magnesium, calcium, and strontium)

Dissenters felt that the -um of aluminum was more in keeping with the oxide's spelling (alumina) as was done for magnesium, cerium, and thorium. They however lost out.

The original US produced of the metal (Charles Mann Hall) seemed to prefer the -um and as as his products was the most often seen, the spelling stuck. American chemists, it should be noted, preferred the -ium spelling in the early part of the 1800's but abandoned it in 1926.
American dictionaries typically label the spelling aluminiumas a British variant. Interestingly enough Canadian spellers are often torn between the two spellings, using -ium or -um in documents intended for internal or external sources by their own arcane rules. The American spelling is winning out.