Turtle Rock is discussing how to address the lack of progression in Back 4 Blood’s solo mode.
As noted on reddit, players who have early access to the game have noticed that when playing in single-player with bots, there isn’t a way to receive rewards unless playing online with at least one other player. In other words, solo mode players won’t earn supply points, which can be spent on cards, which is a main feature of the game.
Instead, solo players have to use solo decks which are a separate system when playing in this mode. Playing in single-player won’t earn players achievements or trophies either, and stats aren’t tracked.