Because most of them are stupid don't have ability to think. As for what I know of this problem, the only explanation is the demanding for tether is very strong, a lot of ICOs depend on the issue of 'currency'. It doesn't only count on US dollars, any other Fiat purchases could contribute to the mint.
I think it's the best thing since Bitcoin because I can use it to save my altcoins when shit start hitting the fan and then buy them when they are low, while Tether pretty much never moves from $1.
Now from my understanding people don't like it because an exchange created this coin and it can be made out of nothing?
But I'm not sure about this.
Any input?