They are extremely complex, but is that complexity required for building a thinking machine? We don't understand bird physiology enough to build a bird from scratch, but an airplane flies just the same.
Are we not just getting lost in semantics when we say "fly"? An airplane does not at all perform the same behavior as a bird. Do we say that boats or submarines "swim"?
Planes and boats disrupt the environments they move through and air and sea freight are massive contributors to pollution.
The complexities of contemporary computers and complexities of computing-related infrastructure (consider ASML and electricity) are orders of magnitudes higher than what was needed for first computers. The difference? We have something that mimics some aspects of (human) thinking.
How complex our everything computing-related should be to mimic thinking (of humans) little more closely?