The most notable refusals for redemptions have been Gemini and Paxos and in both cases it seems it was at least partly to - “maximize their status on CoinMarketCap.”

https://www.coindesk.com/winklevoss-crypto-gemini-gusd-stablecoin-redemption

https://www.ccn.com/paxos-standard-hassling-ethereum-traders-trying-to-redeem-stablecoin-pax-for-dollars/

Would you want your wealth tied up in something worried about how it looks on some piece of shit website?

When you consider how anal they are about conventional banking the anality will go up by an order of magnitude when it's their 'own' money.