I would ask a different question. Why combine a bunch of prices into an opaque number and call it "inflation"?
I'd argue that doing so masks the true causes of price rises. Prices go up because companies make the choice to raise their prices. Sometimes this is because their own inputs became more expensive but in many more cases it's because the people running the company want to increase profits.
By hiding the choices made by people running companies behind this opaque number called "inflation" that people perceive as somehow controlled by the government we've allowed companies to get away with making decisions that increase profits for wealthy executives and shareholders at the expense of people who rely on the goods produced by the companies.
A company normally intends to charge the most profitable price. Ascribing their actions to one force or another is useless, it mainly is supply and demand that force them to set lower prices. When their input costs go up, they raise prices because they otherwise their last product produced would be unprofitable, and when prices go down it is because their customers would go elsewhere if they did not.
I'd argue that doing so masks the true causes of price rises. Prices go up because companies make the choice to raise their prices. Sometimes this is because their own inputs became more expensive but in many more cases it's because the people running the company want to increase profits.
By hiding the choices made by people running companies behind this opaque number called "inflation" that people perceive as somehow controlled by the government we've allowed companies to get away with making decisions that increase profits for wealthy executives and shareholders at the expense of people who rely on the goods produced by the companies.