Currently, “bold” and “italic” markup doesn’t actually output bold and italic text (semantically); instead, it outputs strongly emphasized (<strong>) and emphasized (<em>) text. This is completely wrong and semantic markup abuse, since we can’t guarantee that bold text will only be used for strong importance or that italic text will only be used for emphasis. HTML output for this markup should be changed to general-purpose elements (i.e. *%text%* (_%text%_) should be <i>%text%</i>, not <em>%text%</em>, and **%text%** (__%text%__) should be <b>%text%</b>, not <strong>%text%</strong>).


You’ll need to take this up with markdown-it, which is one of the most popular javascript markdown libraries, and follows the CommonMark spec. They know what they’re doing and I’m sure have reasons for rendering it that way.
Edit: https://spec.commonmark.org/0.31.2/#emphasis-and-strong-emphasis