Staying Awake at Night and Wandering the Road Alone

Avot 3:4

A person who stays away at night, travels alone at night, or turns to idle matters puts his soul in jeopardy.

Abarbanel explains this mishna as a continuation of the previous Mishnayot: talking without Torah, performing an act without Torah, and in this Mishna, the Tanna discusses a person who doesn't use his intellectual abilities (especially during times that are conducive for thinking) to think about Torah.

The previous mishnayot (eating without discussing Torah, two people not discussing Torah) didn't result with jeopardizing one's soul. Why is this more severe?

Delivered at the OU Israel Center, October 29th, 2018 (20 Marcheshvan 5779)