Semantic elements come with built-in accessibility behavior for free: a native button is automatically keyboard-focusable and clickable with both Enter and Space, and announces itself as a button to screen readers, none of which a div requires extra ARIA and JavaScript to replicate correctly.
Using headings (h1 through h6), lists, tables, and landmark elements like nav and main for their real purpose also gives assistive technology and search engines an accurate structural map of the page. Most accessibility bugs in custom-built interfaces trace back to reaching for a div instead of the semantic element that already does the job.