Because words have different etymological roots and different endings can convey different grammatical or linguistic information in many languages? This is just a misguided train of thought comparing the endings of iron and helium and expecting them to be the same. The examples I cited either have Latin roots, or were deliberately latinized words, while Iron comes from an Old English root. Ferrum, the Latin for iron, comes closer to the broader pattern. It's like saying, "I have a calculator that calculates, a ventilator that ventilates, so why is it a phone and not a callator." or something.