2.They are manufactured in china which has cheap labor rates
3.They sell the phones at the same price for a very long time. They don't cut price for very long time there by earning even though they sell at less price
And for the bend gate issue
Every phone will fail a bend gate test I bet. But I am of no concern to those tests because in my daily usage I am not gonna put my phone to those test so I am not worried. From my usage of redmi 3s prime for past year I have dropped my phone quite a lot of time and from quite a large distance too but never did screen crack and sides have small dents only.