Because currently developers can create decentralized stablecoin types that are almost inaccessible to government supervision where fiat stability is precisely the result of government policies. As a result, a portion of the stablecoin's capitalization is not in the fiat reserve records.
because more toilet paper money needs to be printed to back the Stablecoins in circulation.
Decentralization is trust without collateral. When you believe in it, then you must also consider backed assets is valuable even if it's toilet paper.