Bohemia was elevated to a kingdom in 1212 by Imperial decree in response to Bohemia backing the future Frederick II. While there were kingdoms in the Empire, they weren't hereditary lands (which Bohemia was). And most of those longships belonged to the Emperor anyway.

Bohemia was the only imperial state to receive such a boon. Other states aspiring to kingship, like Bavaria, had to wait. Two states circumvented this by becoming kings outside of the Empire, as when the Hohenzollerns declared themselves King in Prussia (which prompted Poland to assert their claim to the Kingdom of Prussia). The Habsburgs also secured the Hungarian crown, though they did so after obtaining Bohemia by marriage (Hungary proved more difficult on account of the Hungarian debacle at Mohacs) -- and Suleyman, as victor at Mohacs, most certainly did not feel that Ferdinand had any right to claim the Hungarian crown. Ferdinand also received the Croatian crown while this all was unfolding.