At some point in the near future, all major online games will need to decide if fabricating the multiplayer experience is in their best interest. Fortnite was the first to fully implement this and it doesn't seem to have negatively impacted their numbers.

What happens when studios start placing bots in lobbies with less than 10 players?

Do people actually care that they are not playing against a real human? The bot backfill in DBD is certainly an early experiment, if not a primer for people to stop caring about who they are playing against so much as the quality of the match.

I don't have an opinion either way. I think DBD specifically could benefit from a fully offline mode that feels like multiplayer, with a "League" mode that is 100% human and advertised as a sort of premier mode for people seeking a real challenge.