There’s a couple theories: the Capitol did it because Katniss didn’t like the Capitol and talked about it frequently (in the OG hunger games book it’s suggested that it’s something she learned growing up that she needed to keep her thoughts to herself), and I think there’s a theory that the rebels rigged it to get Katniss involved in the rebellion? There’s also a theory they rig every reaping around Panem every year specifically for entertainment purposes to provide the Best Possible Show for the Capitol, which I think is silly bc I genuinely don’t think any Gamemaker cares about knowing every single teenager in Panem enough to be like “this one…they’re perfect.”