Why couldn't main memory alone solve the problem of the ROM?

Main memory (RAM) is volatile, meaning it loses its contents when power is turned off, while Read-Only Memory (ROM) is non-volatile and retains data even without power. ROM is essential for storing firmware and essential system instructions permanently, which cannot be achieved with main memory alone. Additionally, ROM is typically more secure against accidental modification, ensuring critical system data remains intact. Thus, both types of memory serve distinct and complementary purposes in a computer system.