There is a long history of free imperial cities having extra privileges within the Holy Roman Empire. Many cities in contemporary Germany, Switzerland, Austria and Italy were former free imperial cities. However, most of them disappeared progressively.
In 1933, when Hitler took power in Germany, 3 free cities remained: Hamburg, Lübeck and Bremen. Unsurprisingly, Hamburg, Bremen are still free cities to this day, which means they are federal Länder states within the Federal Republic of Germany.
What is more of a mystery is why Lübeck is no longer a city state. Actually, the sole reason the city state does not exist anymore and was incorporated into Schleswig-Holstein is because Hitler decided it in 1937, because of his personal dislike of the city (the reason of this dislike is suspected to be because NSDAP support was low).
Despite the fact it was obvious that the dissolution of the city state for such a reason is completely illegitimate, the western allies did not recreate a post-war city state like they did for Hamburg and Bremen.
Are there any reasons the western allies restored 2 of the 3 free cities, but not the third? [*]
Is there any political group in Lübeck that is striving to restore their status as an independent federal state?
It doesn't seem to be the case but I'd just ask in case I might have missed something or used the wrong keywords in German.
[*] I'm excluding Berlin as it has a completely separate history which is out of topic here.