When 8th day Pesach in the Diaspora is Shabbos, Israel and the Diaspora have different sedrahs and eventually the diaspora ’catches up’. Why not catch up as soon as possible to avoid confusion between Eretz and Galos? Why don’t we follow Eretz with its greater kidusha?
ב"ה Shalom You touched upon a question which was asked by Gdolei yisrael generations ago. In Chutz La'arezt they could combine Achrei Mot- Kedoshim so why wait in a leap year (שנה מעוברת) as this year was until Matot- Masei to catch up with Eretz Yisrael.[In a regular year, people in chutz La'aretz catch up Acrei Mot- Kedoshim.] The Magen Avraham (או"ח סי' תכח:ו) based on the Maharit says that the purpose is to have the "klalot"=curses of Bechukotai read before Shavuot with a week break of Bamidbar in between to emphasize that the year and its curses ended[תכלה שנה וקללותיה ] before Shavuot which is like a Rosh Hashana for the fruits on the trees. If Bechukotai were to be read with a longer break of another week, the emphasis of the ending of the year and its curses would not be discerned. However, sometimes in Eretz Yisrael there is no choice but to have Bechukotai read two weeks before Shavuot.( נטעי גבריאל הלכות פסח חלק ג, עמ' רלא) In this case, people in Chut La'aretz cannot follow Eretz Yisrael, due to the lack of Kedusha in Chutz La'aretz which creates a different calendar. This requires those who dwell there to keep another day of Yom tov aspiring to achieve the level of the Kedusha of Yom Tov in Chutz La'aretz in two days, which is done in only one day in Eretz Yisrael. All the Best