But those districts are more scattered around the country and can't be targeted narrowly. They're part of a bigger media market, It's easier for people in adjoining districts to go to rallies, and see the candidates etc. There is more campaign overflow in districts then there is in a state.

While per theoretically it would be a narrower focus the actual result of a district driven election would more mimic a true national election that the state driven election we have now. Purely because there are swing district in more states then there swing states in total.

With a district driven election the candidates would go to Texas, New York and Florida, instead of just Florida.