Because the Church in Rome before Constantine and after Constantine were two different creatures. The term "pontiff" for example was never used by any of the Bishops in Rome before Constantine. It was used by Constantine though and he considered himself to be the "de facto" head of the newly formed Roman Catholic Church. The term "Pontiff" then began to be used by the Bishop of Rome some 40 years after Constantine's death. Many of the traditions of the RCC date back to Constantine and this period of the 4th century and no further.
ROTLFMAO. This all from Constantine's Sword. Your grasp of history is laughable. Constantine the first pope. LOL, that would have been news to Linus and Company. And Sylvester.
So the Church doing some stuff after an event that it didn't do before an event doesn't mean it's a new entity.
Really? Who knew? What factual evidence have you for your fantastic claim that "Many of the traditions of the RCC date back to Constantine and this period of the 4th century and no further."?