Do people here put a ton of money staking stablecoins in sites like nexo, celsius, gemini etc?
Yes, I've seen a group of people that are into staking. They consider those interest rates to be like a steal to them rather than putting their money in the banks.
But the risk is that, they're a platform and they won't issue you your private keys so if you're up to that and good with it, it's your choice to stake with the percentage of APY they'll issue to you but you don't hold the keys.