British royals not attending christenings on their Royal European counterparts is not a recent phenomenom. The Queen Mother had several European royal god-children, Prince Alexander of Yugoslavia, Princess Astrid of Norway, Princess Sophia of Greece ( now Queen of Spain), Princess Benedikte of Denmark ( Ok excuse as it was 1944) and she didn't attend any of their christenings. The only European god-child's christening she did attend was Princess Irene of the Netherlands as that was held in the chapel in Buckingham Palace as the Dutch royals were sheltering in the UK during WW2.
CP Frederik and Prince Felipe didn't attend the christening of their god-daugher Ingrid Alexandra, it's not just British royals who select what social events they'll attend.