Rules of naming ionic compounds
Zinc and cadmium are generally considered to be &quot;almost invariably&quot; in the oxidation state +2 (cfr. the introduction to this paper about one of the few exceptions), therefore the indication of the charge is unnecessary.
Zinc is usually listed as a &quot;Type-I cation&quot; (see Monoatomic ion), i.e. a cation that only appears in one oxidation state, or its case is emphasised as an exception among the transition metals:

Several exceptions apply to the Roman numeral assignment: Aluminum, Zinc, and Silver. Although they belong to the transition metal category, these metals do not have Roman numerals written after their names because these metals only exist in one ion.
-- Chemistry LibreTexts

(For the sake of completeness, the IUPAC Red Book section IR-5.4.2.2 &quot;Use of charge and oxidation numbers&quot; neither mentions &quot;Type I/II cations&quot; nor treats the zinc case separately)