I don't understand why people can't think of BCoB and SCoB as one continuous dungeon split up for the sake of convenience and nothing more. There are lobbies in between but you can do the entire thing without ever going back to the field(same thing as walking through a hall to a different wing after a boss fight) and from what I can tell this is done for a few reasons based on the design decisions in the game.



1. All duties have a timer to prevent a ton of instances being open at once due to people being afk in dungeons for hours. Saving on server power and potentially reducing overall lag.

2. Due to the weekly lockout even if you shoved them all in the same instance and gave it a long clear timer of like 4 hours or something(more than you'd need to clear it but a reasonable amount of time for learning) ALL loot would need to be dropped from the last boss, giving 0 sense of progression and 0 help from drops until you've cleared all the bosses to avoid rampant abuse of clearing some bosses and resetting.(no sol weps, no sands or oils; even if changed to some sort of system where you can only roll the first time you clear a boss that also just leads to different kinds of problems like people selling carry runs for the gear and so on, which Yoshi P. has specifically said they want to avoid from a developer standpoint)

These 2 reasons seem to be pretty big in my book. A potential solution to this would be to save progress like the game already does with t6-t7 trash giving you a shortcut to where the boss is, but from where I stand that's exactly what the game is already doing it's just saving you the hassle of running down all the hallways to where the boss is.