Does anyone invest in stablecoin? I have never heard although it's possible to get a little profit sometimes. However, people use stablecoin to fix their profit or stop their loss by converting their coin to stable. There's no other use of stablecoin then this.
As far as I know stablecoins can actually save us from massive and sudden sideways. Converting our coins into stablecoins will benefit us for volatile market. It is obviously called "stablecoins" because the price is stable and steady. I do not think it can be good at acquiring profits at all except of course for other purposes like keeping in stable price.
In possible case, new investors might be confused and mistakenly invest in stable coins.