Because of elision.
"[Homer wrote] that Achilles died of an arrow in the heel"
This is why the Wiener Kreis taught to use protocolar statements: "<There> and <at that time> <that individual> witnessed <that fact>".
Edit: oh, by the way, in case of interest: https://plato.stanford.edu/entries/vienna-circle/
> "protocoli(s|z)ed"
the use of '-ize' is (a graecism) indicated by the OED as International English, as opposed to British, American etc. In fact, some call International English "British spelling with -ize" - it is not exactly that but close. One exception is 'analyse', but that is because linguists compromised on the "difficult" original 'analysize'.)
It could be. I cannot bring to mind the rules for doubling right now. They both occur, 'protocolar' much more often. I will correct my original post.