Why are these perma-death games popular?
Thread title and your OP cover totally different topics.
Permadeath is one thing, Roguelike not Roguelite something totally different.
Why so many RogueLITE released is a matter of game budget versus game duration. There's been so many because it allows increase duration for a lower budget, it became a good game budget plan for indie dev.
Why so many RogueLITE get fairly successful is like why many players enjoy MMO despite ton of repetitive aspect. A large part of the gameplay fun is transfered from the fun to play, to the fun to achieve.
It's not working well for all players but it did for enough players to generate so many indie RogueLITE.
The wave seems decreasing in my opinion.
True Roguelike are another topic but I doubt it was the topic you aimed. And no, true Roguelike aren't really popular. They require too much effort on design, amount of variations, tuning, procedural management, which let not much money for an AAA polishing level as have all most successful indie games since at least one decade.
EDIT: Combats in RPG are plagued by a similar problem, plenty players don't care that they are tedious, the fun is the achievement to beat the combat thanks to a "perfect" build.