Final answer:
The Frankfurt Parliament lacked legitimacy due to lack of sanction from German monarchs, detachment from the populace, and the refusal of King Frederick William IV to accept a crown from an elected assembly. It also had no means to garner support from key power structures such as the aristocracy and military.
Step-by-step explanation:
The Frankfurt Parliament lacked legal legitimacy because it was an assembly operating without official sanction from the kings and princes of the German states. While the Parliament was created to establish a unified German state and sought to draft a liberal constitution, it ultimately failed to gain acceptance from several critical power structures, including the aristocracy, military, and particularly King Frederick William IV of Prussia. He rejected the notion that royal authority could be emitted from an elected body rather than divine providence.
Furthermore, many of the representatives were divided on key issues, which reflected a detachment from the majority of the population. The Parliament's inability to establish meaningful links with the wider population and negotiate consent from established powers significantly hindered its legitimacy. The aspirations for a unified Germany would later be realized under the more pragmatic leadership of Otto von Bismarck, who pursued a realpolitik approach, rather than the idealistic and liberal endeavors of the Frankfurt Parliament.