I’m not against optional side content dungeons, but I also think SE has the numbers and understands the development time versus average player time engaging the content. I believe they are trying to make side content that a) has more lasting use than a single dungeon and b) can be as future proof as possible and c) is not tied to leveling specifically (once people level the jobs they like, a lot just stop doing certain content).

Just me personally, I found for xp/hour the 50/60/70 roulette was the worst performer, as a result I rarely ran those dungeons. I would not be surprised if others think similarly and that the devs saw a need to make something that offers something other than xp but also a time sink a la Eureka or Bozja or even Blue Mage.