When Israel and the diaspora are out of sync on parshiyot, why don't we take the first opportunity to re-align?

Question

This year (5772) the seventh day of Pesach is on a Friday, so the diaspora has an 8th day of chag on Shabbat but Israel does not. The diaspora will thus read Sh'mini on April 21, Tazria-Metzora on Apr 28, and so on through Bamidbar right before Shavuot. Israel, on the other hand, will read Sh'mini on April 14, Tazria-Metzora on April 21, and so on, waiting until Behar-Bechukotai to split a double (to end up at Bamidbar before Shavuot, as we expect).

There are three double parshiyot between April 14 and Shavuot. I would have expected the first one to be split in order to get the readings back in sync as soon as possible. (This would have meant being out of sync for only two weeks.) Instead, the calendars are not re-aligned until the last of the doubles. Further, if it were a leap year it would be even worse -- we would be out of sync until Mattot-Masei (h/t DoubleAA).

Why do we delay syncing up past the first double parsha?

Answer 1

The reason we have double parshiyos in the first place is in order to satisfy the four basic rules (given in Shulchan Aruch, Orach Chaim 428:4) about the distribution of parshiyos throughout the year. In particular, the first two are: that the Shabbos before Pesach has to be Parshas Tzav in a regular year, or Metzora in a leap year; and that the Shabbos before Shavuos has to be Parshas Bamidbar. Since Tzav is the 25th parshah in the Torah, and Bamidbar is the 34th, and since in most regular years there are only six Shabbasos available between Pesach and Shavuos, then the standard layout is that there are three pairs of double parshiyos during Iyar in a regular year.

R. Yissachar ibn Susan (Tikkun Yissachar) writes, then, that if the people of Eretz Yisrael were to split apart an earlier pair of parshiyos (Tazria-Metzora or Acharei-Kedoshim), then that would imply that they are less important than the Jews living outside the Land (in that they have to change their usual practice for the sake of the chutzniks). Instead, then, they wait until the last available pair (in this case, Behar-Bechukosai) and then split that pair up, because at that point there's no choice - they have to do so in order that Bamidbar be read on the Shabbos before Shavuos.

In a leap year, the people of the diaspora keep Matos-Masei combined to get back in sync because in that kind of year (as in most others) it's normal for Matos-Mas'ei to be combined. (Maharit (2:4) says that we don't combine a pair of parshiyos before Shavuos so that the Jews in the Diaspora (who have the possibility of doing so) can read Parshas Bamidbar in its proper place just before Shavuos, and once we're already pushing it off, we try to place the double parshah as close to the next of the four checkpoints as possible, in order to demonstrate that we are doing so in order to keep to the rules. This could even be why Matos-Mas'ei is chosen in general to be doubled instead of Chukas-Balak in years where we need a double parshah to guarantee proper placement of Parshas Devarim before Tisha B'av.)

Answer 2

I'm summarizing and excerpting some point in my other answer related to this question.

The only requirement in the Gemara concerning Shabbos Torah readings is limited to the need to read certain portions of the Torah prior to Shevuos and Rosh Hashanah, :מגילה לא׃ תניא ר׳ שמעון בן אלעזר אומר עזרא תיקן להן לישראל שיהו קורין קללות שבתורת כהנים קודם עצרת ושבמשנה תורה קודם ראש השנה

The rule states that the "curses" located in Bechukotai should be read before Shavuot. It is unclear if this means immediately before Shavu'ot, or by the time Shavu'ot comes, it should have already been read, meaning that it can be read 1 0r 2 weeks earlier.

Ramba'M adds an additional rule that Va'etchanan should be read on the SHabbat immediately after Tish'a B'Av. (I have to see if he explains why he added this rule.)

By combining these two rules, here's how things work out.

During a non-leap year, in Diaspora, we would need to double Behar-Bechukota to assure that the 1st tochacha is read before Shavuot. (It seems that this needs to be at least 2 weeks before Shavuot and not immediately before.) In Israel, since they were already ahead, there's no need to double up, here.

During a leap year, Bechukotai is already read 2 weeks before Shavuot in Diaspora, so there's no adjustment needed.

However, by the time we arrive at Tisha B'Av, in Diaspora, Matot-Masie need to be doubled, otherwise Va'etchanan would be read two weeks after Tisha B'av and not immediately after. In Israel, since they have been a week ahead of Diaspora, they don't need to double up.

(Incidentally, Matot and Mas'ei are rarely separated. In Diaspora it occurs in leap years when the previous Rosh Hashanna was on Thursday and Pesach is either on Tuesday or Sunday. Same idea in Israel, but they get an extra occurrence on a leap year with Pesach on Shabbat.)