https://news.ycombinator.com/item?id=31381864
Tether is large because it got a head start on network effect before the proper regulatory frameworks were put into place, in the USA at least. There's a massive amount of momentum there even though their product is inferior.
GUSD backing, also audited by a large US accounting firm, subject to New York State Department of Financial Services regulations: https://www.gemini.com/cryptopedia/gusd-stablecoin-gemini-do...
USDP backing, also audited by a large US accounting firm and subject to New York State Department of Financial Services regulations: https://paxos.com/usdp/
DAI backing, viewable transparently on-chain. Currently backed 168% by collateral: https://daistats.com/#/overview
LUSD backing, viewable transparently on-chain. Currently backed 189% by collateral: https://dune.com/dani/Liquity
UST (Terra/Luna) and USDT (Tether) have/had nothing like this.
TerraUSD (UST) was hyped up and became popular mainly because the network paid 20% APY interest on UST deposits, which is a way higher rate on a "stablecoin" than you can get anywhere else (rates in much safer protocols are about 5-8% right now). Obviously a 20% interest rate is unsustainable when it's supported by money printed from thin air. But people were either unaware of this (unsophisticated investors), chose to overlook it (calculated risk-takers, RIP), or positioned themselves to be able to find a chair right before the music stopped (institutional investors like Celsius).