It's private property. If I want to take photos in your front room I probably have to seek your permission and maybe pay you for use because you can't watch TV while I am messing about taking photos.
Shopping malls are designed to encourage people to spend and spill over into other retail or food outlets. If you are expecting to turn up and use it as your personal studio space, without paying you are not contributing to the purpose of the mall. If you are creating scenes with models / tripods then you are a bit of an obstruction to people wanting to spend - more so if there are more photographers with the same idea.
Most places want equitable use of the shared space, so photography rules are mostly to stop people blocking passage. Some IP might be attributed to certain design features.
Most of the time, you can just ask for a permit to shoot for free, so long as you provide proof of your public liability insurance. Some will charge and then you have to decide if that is valuable or you want to shoot elsewhere.
It's common misconception in the UK to think that because somewhere is accessible to the public that it is public space. It's not, they are different. Public space you can shoot, private space you need to seek permission with the owner. Publicaly accessible private space will often have security.
The South Bank in London is all publicly accessible PRIVATE property. You can walk along there, take photos on your phone, eat, drink etc. If you want to do commercial photography, you need a permit. Wedding photographers often get caught out there and will get a bill.