Seigniorage-style stablecoins can’t remain stable forever (forum.stablecoin.fyi)

I mean, collateral is how most currencies used to function. Is there a reason cryptocurrencies can be collateral backed and most other world currencies can't? My understanding is that a gold backed currency becomes much too difficult to maintain at scale, which would eventually become an issue if the currency were to continue growing.

Or I could be missing something that would allow crypto to scale with collateral backing.