it is a good question, how can they sustain the APY offered to their customers?
If they continue to make profits, they will not have a problem because more hot money will flow in and those will remain for a long time, but when problems occur then we will see how strong their financial position is and how well their cash management is.
Therefore, even 8% is not considered high if you compare it to rates, for example, 10% in Binance and others, but the main difference is the degree of solidity of those who print these coins.
I do not think that this is going to be like that. I believe that they are going to end up with something like offering this type of situation for a while and then they are going to drop it and make it more sustainable when they have enough. This is the same with banks, and same with all the other places that offered a high amount return APY for the stablecoins.
Let's assume that you offer 50% for people who put in USDC or USDT and then there are 10 billion dollars invested, and then you drop it to 10% which is sustainable and then there will be some people who leave but you will still have a few billion dollars left and people will not leave. That's what they are trusting it.