Humanoids, in particular, have a lot of moving parts. The human arm has 7 degrees of freedom. The hand has something like 21. Legs, 7. Feet, somewhere between 3 and six. That's a lot of motors, gears, motor controller boards, joint angle sensors, force-torque sensors, etc. Humans have ubiquitous sensing. Tactile sensing of up to 1000 sensors per square inch of skin. Force sensing at every joint. High bandwidth, highly efficient actuators (muscles).

Humanoids are just extremely complicated systems with a lot of moving parts that require very high reliability, along with a metric ton of sensors and the wiring harness needed to support all of it.

For reference, a standard brushless DC motor that is reliable enough, strong enough, and precise enough for use in a robot will retail for around $1000. Just for the motor. And you need at least 30 of them, probably more.