Why do people often capitalize element names?
This is a Google ngram of the usage of the words: iodine, carbon, nitrogen, zinc and Iodine, Carbon, Nitrogen, Zinc (not at the beginning of the phrase).
There is no historical trend, at least not an usage of an archaic form (we can see that the maximum  usage of the capitalized element name is from 1900 to 1960 but normalized to the overall usage is steady).

We can make some hypothesis about why someone could choose to write capitalized element names:

If we must write element abbreviation capitalized (Zn, Cu, C, N) I  can think I have to write the element capitalized even if is not abbreviated.
Someone (me too) may think that if I write Zinc it is more unambiguous and means I'm talking about the concept of element &quot;all atoms with the same number of protons in the atomic nucleus&quot; and not about the metal zinc.  If you write report with some elemental techniques (XRF, AES) sometimes you feel the urge to specify to the reader (that maybe is not a chemist): &quot;when I write that I've found zinc I mean that in the sample could be present $\ce{Zn}$ but also $\ce{ZnO}$, $\ce{Zn+}$, $\ce{Zn^{2+}}$&quot;.
The fact the atoms are identical and the definition of a proper noun is: &quot;a noun that in its primary application refers to a unique entity&quot; could induce to think that elements may fit the definition, and so gain the privilege to be capitalized.
In alchemy elements such water and fire were capitalized.


However up to my knowledge the form not capitalized is preferred even in the others languages, in Italian I'm sure.