1 satoshi/vbyte is like a defaul minimum fee rate by Bitcoin nodes that run by Bitcoin miners. They can config their nodes with lower fee rates but think about their income from mining. It comes from two sources: Bitcoin block subsidy that is fixed, and Bitcoin transaction fees that is flexible and depended on fee rates and transaction sizes of transactions they confirm.

If I am a Bitcoin miner or a Bitcoin mining pool, I have no interest to reconfig the minimum fee rate in my Bitcoin mempool to lower than 1 satoshi/vbyte.