The whole point was to stop people from jumping in and out over and over looking for in-progress.
That was why they added the three strikes thing for declining a readied DF party. (If you ask me though, they could have solved this issue simpler by simply not showing the player whether it's an in-progress group that they got; I would think the three strikes thing had to have involved more programming effort...)

DF lockouts for bailing from a group were a thing before they added the three strikes thing, if I'm not mistaken.

Seriously - do you all have people bailing on your duty all the time?
Yes. It's extremely frequent.

Which just goes to show...

There are consequences. You leave you get 30 minute penalty. I'm seriously having a hard time understanding why people think there aren't consequences already or why more is needed.
I'm seriously having a hard time understanding why you don't understand.

The 30 minute lockout isn't a deterrent. To refer to it as "consequences" is practically a joke.