Why can't gravity be quantized like the other forces?
Quantum fields are usually defined on a spacetime whose causal and geometric structure is supplied. Gravity makes that structure dynamical, so quantizing it also means accounting for the arena used to define the other fields. Perturbative Einstein gravity works as a low-energy effective theory, but it is not a complete high-energy theory with only its original finite set of couplings. OPH proposes approaching the problem from underneath the geometry: quantum observer records should yield spacetime and, under physical entropy and stress premises, Einstein's equation as an equation of state. The analogy is deriving gas pressure from molecules. It motivates a different construction; it does not prove that every attempt to quantize geometry fails, or that OPH has supplied a complete quantum-gravity theory.
See also What is gravity?, What replaces the singularities in the Big Bang and black holes?, Why does the enormous calculated vacuum energy not curve the universe enormously?
Sources: Observer spacetime and the conditional Einstein reconstruction
Also in Chapter 1: Why Is the Universe So Hard to Reverse Engineer?, Chapter 33: Why Was Every Open Problem the Same Problem?.
This answer comes from OPH, Observer Patch Holography. OPH is a rigorous, consistent and complete description of the unified, self-creating computational Universe we inhabit. Its consistency is machine-checked: the fixed point at its core is constructed explicitly, and a theory with a model contains no contradiction.
To understand OPH and check every step yourself, start with the free book Reverse Engineering Reality. It builds the theory from the ground up, and the OPH Notebook answers your questions while you read.
read the free bookask the notebookor ask sage:read chapter 25: Why Does Gravity Look Like Geometry?watch a universe make its own particles