"Used" isn't quite the right word. What you're quoting up there is what's called the long title, an official collection of all the noble titles held by the person.

Francis II's long title would only be used for some official documents, by no means everyday use. Why the long list? Because all those titles were distinct claims directly held by the person of the monarch. For example the titles of "King of Hungary, Bohemia, Dalmatia, Croatia, Slavonia, Galicia and Lodomeria" were all different historic kingdoms and because of that Habsburg rulers had to have several crowning ceremonies.

The crown lands of Bohemia traditionally had a ceremony with the Crown of Saint Wenceslas in Prague, although in reality the heir became monarch as soon as the previous one was dead (Le roi est mort, vive le roi!). Hungary on the other hand required the actual ceremony with the Crown of Saint Stephen in order for the heir to become active ruler; the Hungarian crown as an entity also included the crown and lands of Dalmatia, Croatia, Slavonia, Galicia and Lodomeria.

The title of Archduke of Austria on the other hand is a hereditary title for the whole Habsburg dynasty even if they have just been born. Although I guess the title of Archduke of Austria was de-facto eradicated with Otto von Habsburg signing off any claims on Austria in 1961 so he was allowed back in the country.

I mean if you're the King or the Queen, why do you need any more titles than that? You're already as high as it gets title wise?

The title is certainly nice, which is why it is at the start of the long title. Before the dissolution of the Holy Roman Empire the Habsburg monarchs would even put the kingdoms of Bohemia and Hungary before their "main" title of Archduke of Austria. Still, a kingdom is just one type of land holding.
The Archduchy of Austria was never part of any kingdom. Similarly, Lorraine, Salzburg, Styria or Carintia-Carniola also were independent duchies at one point or another, although Styria and Carintia-Carniola had been under Habsburg possession almost as long as Austria proper. How else are you supposed to show what lands you have if not by having a full list of landed titles somewhere?