Please correct me if I got it all wrong, audited projects are projects that have passed some security checkup right? As a newbie I kinda like investing in projects that are audited atleast so back to my question, USDT is the biggest stable coin right? When I tracked it on coinmarketcap I found out that's it passed audits through Certik and Fairyproof, why haven't this clear the rumour that USDT might fail someday? Because it's Centralised? If that's it then why DAI ( decentralized stable coin) haven't grow over USDT all this while?
I'm not exactly sure what you're talking about, because DAI has certainly grown a lot more compared to USDT in terms of popularity and adoption over the past year or so.
People understand that USDT is a dangerous game to play and they can freeze funds at any stage, which is certainly not a great recipe for holders.
They also run fractional reserve which is exactly the reason why crypto was invented in the first place - to get away from the fractional reserve system whose fragility had brought about the GFC.
I would definitely keep away and invest my own cash in more proven decentralized stablecoins.