The warranty is a very tricky thing. Among other conditions one of the main condition for the validity of warranty is that the car should be fully maintained at 3S dealer and no mods whatsoever, like installing security alarms, alloy rims, tires other than of stock specifications, even using the lubricants, filters used from outside void the warranty.
So the longer the warranty, the longer the 3S dealers get income from maintenance of a car.
About sales, no doubt sales declined after recent price rise, but still there is a long waiting period, means, no manufacturer PS, IMC or Atlas are hit by lack of demand and thus competing with each other.
Atlas never gears their products to beat IMC or PS and the vice versa. They are not competing with each other at all, as all these assembler have steady demand and no surplus products lying in the warehouses.