The answer is economy of scale, the collapse of the American manufacturing industry, bloated budgets, especially brand/marketing budgets, and the prices set by OEM manufacturers who themselves have bloated budgets. A lot of these brands arent actually manufacturers but middlemen for manufacturers. They do design, service, marketing and maybe assembly. But manufacturing is primarily done overseas. If it’s manufactured domestically the labor and material costs are commensurate. Maybe the frame is made domestically, maybe not.
A perfectly decent bicycle is less than $100 in China.