... If that's it then why DAI ( decentralized stable coin) haven't grow over USDT all this while?
The benefit of DAI is that it is all code, there is no business/party that controls it, and that's nice. The downside is that since there are no parties actively controlling it, it is at more risk of losing its peg to the dollar. If we look at the charts we can see that DAI tends to fluctuate a bit more than USDT/C because it is not under the control of a central authority.
Well, that’s what you’re getting when you decide to select a stablecoin that is decentralized.
A stablecoin that is centralized will always have a better control and more pegged to the USD than a decentralized one that has no central authority that controls it. That’s just it, they can both never be the same.
But, with that said, there wouldn’t be that much of a price difference between the two of them, even though that DAI is a bit volatile, the price will still be very close to the US Dollars.