Because they don't replace them, look at Nifty. Last night Nifty talked about how she was missing four items that weren't replaceable. Production even talked about how they weren't going to replace many of Simbal's items with the originals and would instead get him inferior copies from H&M lol. Some items CAN'T be replaced, you could have a watch that was a gift from a family member (in Simbal's case) or a piece of clothing that can't be found in stores (several, in the case of Nifty.) They don't always do it out of maliciousness, sometimes shit just gets given to the wrong people, or gets lost.
Remember that these people have also been in a closed environment full of violence, with escalating tensions, booze and no connection to reality or the outside world for weeks. Shit is crazy. They're told if they can just stay a little longer they'll win, they just have to play the game. Regular people wouldn't allow a 6'5 piece of shit to spit on them to win. They wouldn't endure being constantly recorded or tortured or have their shit stapled to the wall.
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Why would someone bring a sentimental item? Maybe uncle wanted to see it on TV or it was a lucky item. Maybe they wanted to look really good on TV. Who knows. The people going on to TV aren't the smartest anyway.