The 80% of Jews who never left Egypt & who died quietly in the Plague of Darkness were shown all of coming Jewish history: the wandering in the Wilderness for 40 years, the Destruction of both Temples; the massacres, rapine, torture, inquisition, auto da fes, repression, pogroms and Holocaust. And they said "That is too much for us. We want no part of such a Jewish history. We would rather die now!". And they did. Only 20% were prepared to accept the coming tragic & arduous Jewish history, & they left Egypt.
One wonders if we today were given a theoretical choice to relinquish Jewish status (which a born Jew and a bona fide ger cannot do), how many would take the choice: to go from being mediocre Jews to change to being "Good Noahides": no need for Tefillin, Kashrus, Shabbos, Niddah, Davening, Yom Tov, Tzitzits, discrimination, shaatnez, wars, etc and still get some (albeit massively reduced) Olam Habo!
I reckon that now, just as then, 80% of Jewish maaminim in the world would take a get out clause! I asked some yeshiva guys, and they said they would much much prefer to become good goyim at a moment's notice if they could!!