Malbim: There are two reasons. (a) One whose life is a burden on him. He thinks that evils of the world are more than Tovos. (Moreh ha'Nevuchim says that there were groups who held like this.) If so, it is better not to exist than to exist. He curses his parents for causing his existence in this evil life. (b) He wants them to die so he will inherit them soon.

R. Yonah: "Ki Ner Mitzvah v'Sorah Or" (6:23) - a Mitzvah guards one who does it from affliction, just like a lamp's light guards a man from stumbling blocks. However, sin extinguishes a Mitzvah, like Chazal said (Sotah 21a). Therefore, one who curses his parents, his lamp will extinguish, i.e. the Mitzvah of Kivud Av v'Em. Even if he honored them greatly, the Mitzvah will not save him after he cursed them. Chazal said that one can feed his father fattened fowl, and perish due to this ¹ .

Rashi: It is when night and dark come, i.e. when evil comes.

R. Yonah: It is a time of affliction. This is like one who carries a lamp, and when darkness comes, and he needs Regarding the Halachah lamp, it extinguishes.

Malbim: Man's lamp is his Mazal, and success that shines on his head. Even if his lamp is weak or extinguished, he still has some light, like one whose lamp extinguished and he sees via moonlight. This is the hope in every man's heart. However, this one (who curses his parents), his lamp extinguished and he is in darkness without light of hope at all - "v'Ner Resha'im Yid'ach" (13:9), "u'Resha'im ba'Choshech Yidamu" (Shmuel I, 2:9).