This is because USDC is a centralized stablecoin (as is USDT). There are decentralized stablecoins such as UST and MIM (and I believe DAI as well).
Doing so would mean the token could be transacted, except by users who are on the blocklist and not on the allow-list. And this would prevent a privileged user from abusing the power to add accounts to the block-list. Getting unblocked at the speed of DAO is less of a concern, as long as blocked account-holders can still vote with their tokens.