Why use DEX’s?

I'm trying to wrap my head around 1inch, the idea I have is that it is an exchange that incorporates a bunch of exchanges to find you the best value for the swap you want to make.

Right now though I can go on Binance and sell my 1 Ethereum for USDT and then buy DAI with USDT and the fee will be 0.01% on each trade making it like $4 total, but if I want to swap my 1 ether for DAI on 1inch it will cost me $35.

Is this because of Ether fee's being high right now, and maybe when congestion is not such an issue fees will be cheaper than using centralised exchanges, or is there some reason to use DEX today that I'm not seeing? Because clearly millions of dollars are being exchanged on 1inch but I can't see why if it's cheaper to use Binance or something like that.

tl;dr: please help me understand the value of DEX's as they stand today with high fees.

Thanks so much for any help