Why do we need stablecoin when we already have bitcoin and probably other cryptocurrency that can be used to pay for the groceries. Don't forget stablecoin weren't introduced into the industry to replace bitcoin and other currency but was introduced due to the need to minimize losses when the market is experiencing a downward movement.
You've just answered your own question. People prefer holding stablecoins during bear markets (like the current one) so they can hedge BTC's loss in value. It's a hassle to convert back to BTC every time they spend, not to mention the added costs from trading and withdrawal fees.
I think this is part of the rationale behind Bitpay recently adding support for stablecoins.