R. Aha said: From where did they receive what was theirs (their due punishment)? It was simply that they did not occupy themselves with being fruitful and multiplying. They were saying: We are buds of the high priesthood, so should we take wives who are not worthy of us? R. Aha said (in the words of Ps. 78:63): "FIRE DEVOURED THEIR YOUNG MEN." Why? Because (ibid.) "THEIR MAIDENS HAD NO NUPTIAL SONG."
Why Fire Devoured Aaron's Sons Who Spurned Marriage
Midrash Tanchuma Buber, Achrei Mot 13:2
ר' אחא אמר מהיכן נטלו את שלהן, אלא שלא נזקקו לפריה ורביה, היו אומרים אנו פרחי כהונה גדולה, ואנו נוטלין נשים שאינן הוגנות לנו, אמר ר' אחא בחוריו אכלה אש (תהלים עח סג), למה בשביל בתולותיו לא הוללו (שם).