A fully autonomous stablecoin smart-contract is like a self-driving car. Asking who is issuing the stablecoins is like asking who is driving a self-driving car. The answer is the contract itself in the former case and the car itself in the latter case.
Considering the developers of an autonomous stablecoin smart-contract to be the issuers of the stablecoin would be as incorrect as considering the manufacturers of a self-driving car to be drivers of the car.
Note that full autonomy and immutability are required for this interpretation. If there are entities capable of interfering with the execution of the smart contract, including by having the power to upgrade it and change its code, then those entities ought to be considered issuers, similarly to how anyone capable of overriding a self-driving car's driving algorithms ought to be considered a driver.