Question: Why was Frederick I only called "King of Denmark" while Christian III was named "King of Denmark and Norway"?

Context articles: Hesselagergård
Christian III of Denmark
Count's Feud
Vincens Lunge
Christian III (disambiguation)
Treaty of Speyer (1544)
Frederick I of Denmark
Juliana Maria of Brunswick-Wolfenbüttel
John, King of Denmark
Election of Christian III

Hesselagergård (or Hesselager Manor), located near Gudme in the southeast of the Danish island Funen, is the oldest Renaissance building in Denmark.
 It was built by Johan Friis, one of the most powerful men in Denmark during the reigns of Christian III and Frederick II.
Christian III (12 August 1503 – 1 January 1559) reigned as king of Denmark from 1534 until his death and Norway from 1537 until his death.
 During his reign, Christian established Lutheranism as the state religion within his realms as part of the Protestant Reformation.
The Count's Feud (Danish: "Grevens Fejde" ), also called the "Count's War", was a civil war that raged in Denmark in 1534–36 and brought about the Reformation in Denmark.
 The Count's Feud takes its name from the Protestant Count Christopher of Oldenburg, who supported the Catholic King Christian II, deposed in 1523, over the election of Christian III.
Vincens Lunge (sporadically referred to as "Vincents Lunge"; c. 1486 – 3 January 1536) was a Danish noble, member of the Norwegian realm council ("Riksråd") and the foremost representative of King Christian III of Denmark in Norway.
Christian III generally refers to Christian III of Denmark.
 It may also refer to:
The Treaty of Speyer or Peace of Speyer was signed on May 23, 1544 between Denmark and the Holy Roman Empire during an Imperial Diet of the Holy Roman Empire in Speyer, Germany.
 Danish king Christian III had imposed heavy tolls on the Sound and two other channels between the North Sea and the Baltic sea, in an effort to end the Dutch dominance of trade in the Baltic region.
 Under pressure from Holy Roman Emperor Charles V, he agreed to exempt the Dutch ships from these tolls and give them free and unfettered access to the Baltic.
 In the treaty, Charles V also recognized Christian III as the rightful king of Denmark, and promised not to provide military support to his rival Christian II.
 The Treaty of Speyer dictated Christian III's foreign policy for the rest of his life.
 He kept Denmark at peace, refusing to involve the country in Protestant-Catholic conflicts such as the Schmalkaldic War of 1546.
 The Dutch would continue to dominate Baltic trade for another two centuries.
Frederick I (7 October 1471 – 10 April 1533) was the King of Denmark and Norway.
 His name is also spelled "Friedrich" in German, "Frederik" in Danish and Norwegian and "Fredrik" in Swedish.
 He was the penultimate Roman Catholic monarch to reign over Denmark, when subsequent monarchs embraced Lutheranism after the Protestant Reformation.
 As King of Norway, Frederick is most remarkable in never having visited the country and was never being crowned King of Norway.
 Therefore he was styled "King of Denmark, the Vends and the Goths, elected King of Norway".
Juliana Maria of Brunswick-Wolfenbüttel-Bevern (Danish: "Juliane Marie"; 4 September 1729 – 10 October 1796) was queen of Denmark between 1752 and 1766, second consort of king Frederick V of Denmark and Norway, mother of the prince-regent Hereditary Prince Frederick of Denmark and Norway and herself de facto regent 1772–1784.
 King Christian VIII of Denmark descends from her.
John (Danish and Norwegian: "Hans" ; Swedish: "Johan" ; né "Johannes") (2 February 1455 – 20 February 1513) was a Scandinavian monarch under the Kalmar Union.
 He was King of Denmark (1481–1513), Norway (1483–1513) and as John II (Swedish: "Johan II" ) Sweden (1497–1501).
 From 1482 to 1513, he was concurrently Duke of Schleswig and Holstein in joint rule with his brother Frederick.
 He currently remains the only King of Denmark since the mid-15th century to not be named Christian or Frederick, if one does not include the current Queen of Denmark, Margrethe II.
The election of Christian III as king of Denmark and Norway on 4 July 1534 was a landmark event for all of Denmark and Norway.
 It took place in the church in the town of Rye, eastern Jutland, where the Jutlandic nobility elected Prince Christian, son of King Frederick I and Duke of Schleswig and Holsten, as king.
 This brought about the Count's Feud ("Grevens Fejde") and later also led to the implementation of the Protestant Reformation in Denmark and Norway.