Why Is It Called Lag Ba'omer if it Should Really Be Called Lag La'omer?
The Kuntras "Hod Shebehod" (p. 26), asks the following question (summarized):
Question: For those who follow the Ariza"l and insist on saying "La'omer" when counting, why is the 33rd day called "Lag Ba'omer"? Shouldn't it be called "Lag La'omer"?
The following various answers are presented (summarized):
Rav Moshe Tzuriel Shlit"a: Really, the Sephardic way to say it (La'omer) is correct, but since Ashkenazim ruled over most of the institutions, their way won out in the end.
Rav Eliyahu Maman Shlit"a: Sepharadim in fact do say "Lag La'omer". [YY - I can attest that in some circles, this is 100% true.]
Rav Yisrael Chaim Blumenthal Shlit"a: The 18th of Iyar is the Rema's Yahrtzeit, so we follow his opinion on this day only and call it Lag Ba'omer.
Rav Uriel Shalmoni Shlit"a: The Shulhan Aruch never mentioned "La'omer" - in parentheses, they added "Ba'omer" and see the Mishna Berura S"K 8, who says that many say "La'omer", but obviously, it doesn't prevent you from fulfilling the Mitzva either way. So it appears that the holiday was called "Lag Ba'omer" by those who said "Ba'omer" and everyone was dragged along after them, but we don't need to start looking for reasons. (There's a Remez: ל of La'omer + the ב of Ba'omer + the Kollel = 33.)
Rav Gamliel Hakohen Rabinowitz Shlit"a: I thought about this question in the past and I'll need to look for what I thought about this. But now, I thought about a Hiddush in Halacha: that according to those who say "La'omer", if he tells his friend on Lag Ba'omer night, "Tonight is Lag Ba'omer," he may still say a Beracha according to all opinions since by saying "Ba'omer", he is revealing his intention of not fulfilling his obligation with that statement. וצ"ע. [The footnote on the page, however, says that according to Rav Avraham Halevi Lifschitz Shlit"a, there is no difference between whether one says La'omer or Ba'omer.]
Rav Shmuel Baruch Ganot Shlit"a: [He doesn't really answer the question, but poses another related question.] The Tzemah Tzadik (of Vizhnitz) asks: "Why do we call it ל"ג "Lag"? Since we count with the smallest number first, e.g. "Today is 3 and 30 days", [it should be called ג"ל "Gal Ba'omer"!] Perhaps, we can say that the main idea of Sefirat Ha'omer is to purify physicality and thereby have the aspect of מה, since the intent of the Sefira is with שם מ"ה as is known. And then, on Shavu'ot, he will merit to come to day 50 which corresponds to the gates of Binah. With this, we can explain the gemara (Berachot 56b) that says that one who sees reeds (קנים) in a dream should expect Binah because in Ta'anit 20a, it says that a person should always be soft like a reed (קנה) and 2x 155 (gematria of קנה) equals 310 = עמר (Omer), so one who sees reeds in a dream should expect Binah. Therefore, we call it ל"ג בעומר Lag Ba'omer because the letters between the ל and the ג [when you continue from the end to the beginning] is מנסע"פ צ"ק רש"ת א"ב, which is the gematria of 1393, the gematria of כת"ר שב"ת הוי"ה מ"ה, since this is the main intent of the Sefira - to merit the כתר שבת only for Hashem's sake - by having the aspect of מ"ה which is hinted to in the Sefira. And only then will he merit ג"ל - meaning, the letters between ג and ל [which are דה"ו זחטי"כ] whose gematria is 69, which is the gematria of חיים with the Kollel since it draws life from the Tree of Life. Altogether, 1393 + 69 = 1462, which is the gematria of 5x גבורה [???] which is sweetened with the 5x חסד [x4], whose gematria is 1440. There are 22 left over, hinting to the 22 letters of the Torah, and that explains Tehilim 118:18 ג"ל עיני ואביטה נפלאות מתורתך."
Rav Kfir Baruch Mevorach Dadon Shlit"a: The first Rishonim to mention Lag Ba'omer are Ashkenazim: the Sefer Hamanhig, the Maharil, etc. So since they mentioned the holiday first, the name stuck.
Rav Sha'ul Gordon Shlit"a: To honor the Rema, whose Hilula it is, who said "Ba'omer" (brought down in the pamphlet "Damesek Eliezer" by Rav Alexandar Eliezer Knopfler Shlit"a, Behar, 5774)
Rav Moshe Wolf Rosenberg Shlit"a: I saw in the pamphlet "Ner Hahaftarot" who brings in the name of the Satmar Rebbe ZY"A that we do so to honor the Rema on his Hilula day.
Rav Mordechai Almakiyas Shlit"a: 1) Because the main people who went to Meron were Ashkenazim. 2) Rashei Teivot of ל"ג בעומר is לב, meaning that on this day, holiness and enthusiasm enters man's heart. 3) Those same Rashei Teivot are the letters that begin and end the Torah, hinting that Lag Ba'omer is like a Matan Torah of Nistar.
See there for other interesting Lag Ba'omer questions.
[See lyrics of songs for Lag Ba'omer here and here. See Piyut's versions of some of these songs here.]