From a theoretical point of view you can see this as the fact that the 3 standard model interactions are forces (they generate 1D displacements), while in general relativity gravity exerts deformations* (which are described roughly as 2D displacements).
1D displacements are described by vectors (i.e. spin-1 objects) while deformations are described by particular rank-2 tensors (i.e. spin-2 objects). This is the reason.
Why gravity does exerts those deformations instead of forces and is so different is yet to discover.
*Deformations are intended, roughly, as the application of force in 2 different directions, usually not collinear, so that it deforms the path and shape of objects immersed in the gravitational field