While I’m not knowledgeable on all the factors, part the reason he wasn’t able to get an annulment was because Catharine’s nephew, Charles V (King of Spain Holy Roman Emperor), had influence on the pope and didn’t exactly like the idea of his aunt being divorced, hence why Henry VIII broke away. From a history class I’ve taken, I learned Henry VIII did have affection for Catharine, but the need for a boy (to avoid the throne going to a Scottish king) was what drove him from Catharine when she was older.
Side note, here’s what a source gave for Charles V’s full title to give you an idea of how much he ruled: Charles, by the grace of God, Holy Roman Emperor, forever August, King of Germany, King of Italy, King of all Spains, of Castile, Aragon, León, Navarra, Grenada, Toledo, Valencia, Galicia, Majorca, Sevilla, Cordova, Murcia, Jaén, Algarves, Algeciras, Gibraltar, the Canary Islands, King of Two Sicilies, of Sardinia, Corsica, King of Jerusalem, King of the Western and Eastern Indies, Lord of the Islands and Main Ocean Sea, Archduke of Austria, Duke of Burgundy, Brabant, Lorraine, Styria, Carinthia, Carniola, Limburg, Luxembourg, Gelderland, Neopatria, Württemberg, Landgrave of Alsace, Prince of Swabia, Asturia and Catalonia, Count of Flanders, Habsburg, Tyrol, Gorizia, Barcelona, Artois, Burgundy Palatine, Hainaut, Holland, Seeland, Ferrette, Kyburg, Namur, Roussillon, Cerdagne, Zutphen, Margrave of the Holy Roman Empire, Burgau, Oristano and Gociano, Lord of Frisia, the Wendish March, Pordenone, Biscay, Molin, Salins, Tripoli and Mechelen.