Why do retailers discount heaviest near Christmas, when demand is highest? Why are such discounts larger in electronics and apparel than in automobile?

Demand Curves

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Why do retailers discount heaviest near Christmas, when demand is highest? Why are such discounts larger in electronics and apparel than in automobile? What are such discounts almost non-existent for baby items?

Why are there so many different types of cereal, although very few cereal manufacturers? Why are there so few types of computer chips, while also few computer chip manufacturers?