Neither of those statements is true. Bitcoin seized by US government is often sold off in auctions[1]. Tether seized by the government could also be redeemed for fiat eventually, following due process.

[1] - https://www.forbes.com/sites/brandonkochkodin/2023/03/31/us-...

EDIT: I see now that you were actually comparing the case of USDT freeze against Bitcoin seizures. Nevertheless, Tether doesn't simply get to keep the USD value of the frozen tokens. US government would want to recover that.