Time limit to re-enter dungeons

[Amineri]

you enjoy finishing all content in 1 week and then waiting 2 months for new stuff to be added?

I'd guess the reasoning behind this is:

Play However You Like
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All of this means big changes to the game’s balance, aimed at giving players the freedom to play however they like. I know there are players out there who are too busy irl to spend a lot of time playing during the week. No problem! Use your anima to get you where you need to go. Maybe you have more time to play on the weekends? Great! Mount up and travel around Eorzea with your companions on chocoboback, or grab an airship! This is the kind of freedom I want you to have—the freedom to choose your own style of play. And it is going to be a major focus of FFXIV’s development from here on out.
...

Those who can only play once per week can choose to run through the dungeon seven times in one day, rather than being limited to once per day (and hence once per week in their case).