Theory Of Everything was first used satirically. Though, thinkers since at least the ancient Greeks have pointed to the possibility of and need for one. The known fundamental forces were for a long time thought to be simply seperate. But then electricity and magnetism were unified. Then in the search for unifying electromagnetism with gravity, the strong and weak forces were discovered. And the electroweak force, was found to unify electromagnetism and weak nuclear force at higher energies, making a model for expected unification of the other forces, at higher energies. In particular, the theories with the greatest explanatory power, general relativity and quantum field theory, can niether account for black holes where the energy levels and scale require information from both, which contradict each other.
So, historically, unifying fields has been a result rather than an expectation. Although, the scientific view presupposes substance monism; matter, energy, and to some extent space have been unified. We expect that in blackholes and the early fractions of a second after the big bang, that this unity of substance will be manifest and result in the patterns and behaviour we see. Expecting substance monism is really expecting explanatory unity
David Deutsch objects to a Unified Field Theory being treated as a Theory Of Everything. He suggests four domain-specific are essential for understanding everything, epistemology, computation theory, evolution, and the many worlds interpretation of quantum mechanics. Information certainly has fundamental consequences in physics, from entropy to event horizons. Deutsch argues that life is also fundamental, it's possibility and specific occurences, to understanding causal behaviour. And epistemology links minds to worlds.
Theories of Everything, generate diverse phenomena from simple axioms. Godel's Inompleteness Theorem deals a devastating blow to this model of explaining things, finding that the behaviour of an axiomatically derived system is not fully determined by it's axioms. This suggests that a Unified Field Theory would not be a Theory Of Everything. This line of reasoning convinced Hawking there would not be a TOE. However, reasonable objections can be made about explanatory power, vs decidability. This may allow emergent systems -like life- to not be fully accounted for by a UFT with explanatory power to account for all the fundamental physics. So, requiring domain-specific theories. This can also further be supported by the idea any theory has limits to accuracy, and theoretical models should not be confused with reality.
The idea that physics has fundamental explanatory power, presupposes hard reductionism - which we have good experiences with, but no deep evidence for. It has computability on it's side, but really nothing deeper.