According to Chazal we have this 80/20 phenomenon in Bavel and Mitzrayim, or in other words, only 1 in 5 came out. What is the reason for this ratio in Kabbalistic reasons and it seems to be repeating yet again?
--Snip from-- Who is in Charge? HaRav Boruch Medan
"There is a tradition in the name of the Chazon Ish that before Moshiach comes, four-fifths of the Jewish people will perish, and only a fifth will survive (based on "the Bnei Yisroel went up armed [chamushim -- can also be read as "one fifth" -- see Rashi] out of the land of Egypt"). Tzaddikim will have the merit of being amongst this fifth. A tzaddik is someone who strives to serve Hashem properly, who knows how to grow in Torah, and understands that there is nothing as important as Torah.
Chazal have assured us that during the ikvesa demeshicha every person who deals in Torah and chesed will be saved [“Rabbi Elazar was asked by his students: what will a man do to be spared from the pains of the arrival of the Mashiach? Let him occupy himself with the Torah and let him perform acts of kindness” (Talmud Sanhedrin 98a) ]. We must wake up from our slumber! We have to learn Torah and run to do chesed!"
Regarding a Kabbalistic reason, From vague memories (I can't remember the sources) a. Those 80% would have to reincarnate--they weren't refined enough to tolerate geula at that time..not enough emuna, etc. b. I've seen various sources the majority of Jews, especially in this generation are from the erev rav (usually 2/3rds are cited--I asked a mekubal if the numbers are "that bad" and he said "yes, they're that bad.")