Posted on: 02/23/21 02:31AM
There are a few reasons. Here are two important ones:
Linking the post page allows the user to find more artwork by the same artist to get to the original artwork's source, and to interact with the post page on the site (commenting, favoriting, upvoting, etc). A direct image link does not.
Links to post pages are permanent. For the foreseeable future, any link to a post page, especially if you use the post BBCode, will always work and take you to the specified post so long as that post still exists on the site. A direct image link is not. In fact, we just recently changed image servers, which caused most direct image links already out there to stop working. We've had no fewer than 10 users come ask for help because their direct image links and bookmarks broke. This wouldn't have happened if they used post pages rather than direct image links.
There are a few additional reasons that aren't of direct consequence to you as users, but they are important to us as site staff. Because of these reasons, we ask you not to use direct image links. This doesn't just only apply when you're on Gelbooru; please do not post direct links to Gelbooru images on other sites or communities either. Always link the post page.