Why can't I sell HEX on Uniswap?

Excuse me, I'm having some trouble understanding why I'm unable to sell HEX tokens on the Uniswap decentralized exchange. Could you please clarify why this is the case? I've been looking forward to trading my HEX holdings for other cryptocurrencies, but the option doesn't seem to be available. Is there a specific reason behind this limitation, or am I missing a step in the process? Your insight would be greatly appreciated.