Really to do things right you need a footing at least 8 feet deep if more. It's hard to do just a slab and have it not crack. That's why you see sidewalks and pavement cracks all the time, those are just slabs put on the surface. They do their best but it's always going to move a bit from the frost.
Deep footings are one way that works well but are not necessary. A large slab can also be designed to float, for ex. on sand, clay, or permafrost. The additional reinforcement expense is often less than constructing a deep foundation wall.
In the commercial and industrial construction world there are rarely any issues with concrete. It is backed by thoroughly understood math/science. On the residential side problems occur only because the customer often demands low cost above all else which leads to low barriers for contractors to enter the market.