That's because it is cheaper to acquire land than build underground parking. I live in a city that has gone through that transformation. Big parking were converted into malls/supermarkets with multi-floor parking.
Parking areas were also built with underground parking buildings. But that's only because land become scare and so it was expensive to have a non-underground parking.
Parking areas were also built with underground parking buildings. But that's only because land become scare and so it was expensive to have a non-underground parking.