Yeah one of the biggest issues w/all the different options for stablecoins is that its just spreading liquidity thin across a bunch of base pairs. When it was just USDT that was great since it had lots of volume. Unless exchanges decide to really care that DAI is the most ideal approach to a stablecoin, I don't think it will be a viable trading pair until the overall market has a LOT more liquidity and volume.
That won't happen. The exchanges are all incentivized to promote their own stablecoin, like Coinbase paying interest on USDC now. At the least, they are earning interest off stablecoin holders, but more importantly, they are keeping traders oriented towards their own market liquidity. Coinbase wants you to stay in the USDC markets, not withdraw DAI to competing exchanges.