Jews died in plague of Darkness because they were being frum

 Rav Yaakov Kaminetsky (Emes L’Yaakov Shemos 10:22) Rashi states, “Why did G-d bring about the plague of Darkness? Because the Jews in that generation were wicked and did not want to leave Egypt and therefore thousands died in the three days of darkness.” So even though that in reality that entire generation were not considered righteous (tzadikim) as we see the angels claimed that both the Jews and Egyptians were idolaters – so why kill the Egyptians to save the Jews. In other words the angels could not see the slightest difference between the Jews and the Egyptians and thought all should die. And thus the Jews that died were apparently killed entirely because they were preventing the other Jews from leaving Egypt because they had a tradition that the Jews must remain enslaved in Egypt for 400 years and since the time had not passed they were afraid that they would suffer the fate of the Ephraimites who left prematurely.

 They thus did not believe the words of Moshe and the Elders that G-d's calculation was based on the merit of their forefathers. Therefore G-d killed only those but not all the Jews even though in the eyes of the angels they were all idolaters. Only G-d was able to distinguish Jews from the Egyptians and know that the Jews would eventually be capable of accepting the Torah at Sinai  This inner nature of the Jews was not noticed by the Angels and G-d had to prove it by showing the Angels Yosef’s coffin [Bereishis Rabbah 7:8] that Jews were inherently different. [See my previous comments to Shemos 13:9]..[to be continued]