Shallow foundations are preferred where soil close to the surface is capable of supporting structure loads.
Where the ground close to the surface is not capable of supporting structural loads, hard strata is searched for and deep foundation is required.
Uniform stable ground requires relatively shallow foundation whereas filled up ground has low bearing capacity thus requires deep foundation.
On the basis of Loads from Building:
In the case of low-rise building in a larger area, the extent of loading is relatively low, so shallow foundation can resist the load from the structures.
In the case of the high-rise building built within less area have high loads. Therefore, the deep foundation is required as shallow foundation may not be able to resist such loads of greater intensity.
