No quail experience, but I wonder how much is just due to the size.
Being so small, they have less body mass to help regulate heat, and walking just a few inches back to the heat source takes them a lot more steps than for bigger chicks.
Being small also means less size/fat/resources to get them through an extra day or even few hours of learning how to eat and drink.
Being so small, they cannot reach some food/water dishes, and even the chick-sized waterers are plenty big enough to drown quail. If you try to use a bottle cap for water, you may solve the downing problem but then it evaporates really quickly and they go thirsty.
Also, chicken food is pretty easy to get, but the quail need a higher protein, so getting the right food is harder. And it needs to be in really tiny pieces, too.
Yes, I know there are solutions for all of these things. But the more things you have to solve, the harder it is to raise that kind of bird. And they're so small, they have less resources to survive the time it takes to recognize a problem and find a solution.
Those are my guesses (They are also some of the reasons I have not yet tried raising quail myself )