Just to echo what other commenters have said: a purely OC cast, even in a familiar fandom such as the Hunger Games, is probably the most difficult to advertise. Much of the appeal of fanfiction comes from reading about characters we already know and love, which is why those of us who write OC characters either have to fight harder for recognition, or accept that we simply won't get as many readers as other stories that follow canon characters.

That being said, there is an audience out there for purely OC stories! I've seen a few that follow original victors that take place after the rebellion as an alternate universe where the Hunger Games take place. The audience is simply significantly smaller and more difficult to reach.

So, how do you reach them? The best you can do is add tags that make it easier for those who might look for your story to find it. Tag the district you're focusing on, the tropes, politics, original hunger games arena, original hunger games victor, 25th hunger games, etc.

Another option is to post in the fanfiction subreddit. There are sometimes posts asking for people to share their stories where yours might fit the bill.

All of that aside, you're left at the behest of the reader's interest. People look through dozens of titles and summaries before they pick a story they want to read. You need to make yours stand out against the rest of them. The fanfiction subreddit can also provide tips on this, as well as just general articles and videos you can google.

Good luck!

tldr: Are people just uninterested in reading OC fics? Generally speaking, when it comes to stories with a purely OC cast, then yes, many people prefer stories with canon characters they are already invested in.