Hello!
The Listing map, when used on the Listing pages, displays the number of posts as set by the WP Blog “Posts per page” settings, as Kor mentioned. This is by design, and there are no workarounds; changing the behavior would be a customization. You can, however, as Kor stated, add a map to a different page.
All that said, a member did provide a snippet that you could try; the snippet overrrides that WordPress setting:
https://wpgeodirectory.com/support/topic/show-all-listings-on-map/#post-16449
This snippet is not recommended, though. There are several other maps that display ‘all’ including the Home page map and the Location pages, but the listing page and your site’s performance may be seriously impacted by the snippet mentioned above.