Change The Rules For Leaving Dungeons (aka Why People Insta-Quit Castrum Meridianum)

[Deceptus]

Or improve the rewards to make running Castrum more appealing instead of how it feels now, which is the "ugh I could've had Prae" roulette sink
Make a forced delay on when you can leave and you just end up with people refusing to move and asking to be kicked more often, probably. That already happens now with people not wanting to eat the 30 minute timer.
Also, some dungeons (a lot of dungeons if the group is good) literally take like 15-20 minutes so you'd be effectively locking people in for the entire dungeon regardless of what may or may not happen - including irl stuff. Again leaving somebody as afk deadweight and requiring a kick.

This. People quit because they don't think the reward is worth the effort / time investment.

That's purely on the SE Dev team.