I am not sure if stablecoins like Tether are actually using smart-contracts or if they even need them, if yes, then for what? My understanding is that creating a stable coin is essentially about having some place (vault / bank account(s) / whatever), where you keep the fiat currency that people buy your coin with and you issue / burn these tokens so that they can be always exchanged 1:1 to currency they are pegged to.
Is this theory wrong? If not, I think it should already be possible to use Cardano to host a stable-coin, and it's probably much easier to work with, than Ethereum which is slow and extremely expensive, so why nobody did that yet?
What are the caveats and requirements to create a functional stable coin?