Bro, I think, tires traders and mechanics themselves do not know the drawbacks of installing them, since hardly anyone of them will be Automobiles engineer. Some can be Diploma holders (DAE, B Tech. etc.), but chances are quite less.
Used JDM cars have low ground clearance, and in some cases, like Aqua and Prius, I think, spacer springs / packing becomes necessary, since tires / rims up-sizing alone does not prove sufficient. But traction control gets affected after installing them, and handling and driving control at high speeds also becomes difficult.
There is nothing wrong with these cars. These are the car breaker type speed breakers here, which prove disastrous for the cars. They are made without any planning and design. Jub, jiska, jaisay dill chahta hai, bnaa daita hai, and the situation is even worse in Galli, Mohhallas (No offense / disrespect).
If they are made with proper planning, I hardly think anyone would go for spacer springs / packing.