They don't, because there is not such thing as fungibility. One coin is, and should be equal with any other. Period. The only ones who disagree with this principle are exchanges that cooperate with surveillance companies, and which enforce completely arbitrary rules. They blacklist coins that are CoinJoined, PayJoined and mixers' UTXOs, so it won't surprise me if they asked to provide further info because "input silence".

You were probably referring to privacy.