I think a big reason Electrical and Computer engineers expect that we will understand or at least replicate the human brain in the electrical domain is that we've seen impossible-to-understand systems tamed and replicated before: transistors.
Transistors are bundles of impossibility, where quantum mechanics are needed to even understand the basic operating principles, and to really design them, one must confront problems of such awe-inspiring complexity that it's hardly a surprise we are often the ones who go a bit mad.
And yet every day, trillions of these impossible boxes are instantiated, reproduced, copied, pasted, and spun like it was nothing. Unconsciously. The impossible box becomes a normalcy. And if we can do that, they imagine, why not the same with a similar system made out of gels and fibers?