At least some part of thought is physical, or things like transcranial magnetic stimulation could not happen.
And modern animal behaviorism, neurology and evolutionary psychology have given us a lot of indications that many of the reasons for the ways we think can be explained in terms of survival and other aspects of biology. The first part of Dennet's Consciousness, Explained collects up a bunch of those, and points at others.
So, what is the resistance to imagining that the rest of thought can be explained by physiological processes?
The more important question isn't whether this is true. The question is whether it is relevant. Many people accept that thought is caused by complex phiological functions, but consider it an 'emergent' phenomenon.
Other examples of emergent phehomena are things like heat, acidity and molecular bonding. Each of these things has an accepted underlying explanation in a lower level of physics. And yet we cannot use that lower level explanation. There is too much complexity involved. It is nice to know that heat is explained by molecular motion, but we do not measure it that way, and we do not think about it in those terms when we do thermodynamic calculations. We think in terms of entropy, flow, conductance, etc.
Apart from theorems that tie the base cause to the basic principles through statistical mechanics, we never think about heat that way at all. We largely use principles from Carnot, someone with an entirely different underlying theory of heat, as a subtle substance.
Likewise, is it even helpful to work out the mechanics of thought? Or should we presume it will be as useful as measuring Brownian motion when you have a thermometer? The alternate view points out that we already know a lot of things about thought from an internal viewpoint. Why not use that information as our basis instead of pretending that we learn about thinking by observing others? Because we just don't.
So it makes some sense to purposely not bow to the obsession with 'objectivity' that makes us consider alternative formulations misguided. If the real information should come from inside, emergentism is just a sop to throw to materialists. It doesn't gain us anything but an illusion of peace. What is solves is a non-problem.