Linked from
The 30 pages that link to String theory, each with the reason it gives.
Quantum gravityRelated: It incorporates gravity by including a massless spin-two string mode.
SupersymmetryRelated: Supersymmetry became central to consistent superstring theories.
GravitationRelated: It includes a quantum description of a particle with gravitational properties.
Modern physicsRelated: It is one candidate approach to unifying quantum theory and gravity.
SupergravityRelated: Supergravity theories describe low-energy limits of string theories.