Why refigerant distributor from Brass material but not copper

Cost, mechanical resistance and manufacture processes are good reasons. And, the distributor does not have to be that optimum thermal conductor itself.

Adding to bhrescobar's GA, brass (bronze also) is more easily produced and machined in solid shapes, such as refrigerant distributors, than copper is. Copper is great for wire and tube, but brass and bronze are better for molding, casting, and machining.