If they wanted people to use a different tag for such text, they should have created an idiomatic tag instead of attempting to repurpose existing ones.If you read the spec, it mentions several different uses for <i>, depending on the context. Otherwise, we’d need a different element for each context, bloating the spec by having special purpose elements instead of general ones.
For example, <i> is used for ship names:
<p>They came over on the <i>Mayflower</i>.</p>
It wouldn’t make a lot of sense to have an element
just for names of ships in a general purpose markup language like HTML.
Turns out, if you look at the Wikipedia article about the Mayflower, the name is marked-up with the <i> element [1].
[1]: https://en.wikipedia.org/wiki/Mayflower