I saw a great suggestion in some youtube comments that I can't find here, and have built on it.
I think having some kind of mission progression that improves the town you are in, maybe this starts after you have cleared blood plague or in parallel with it, for example:
1. Protect community members while they repair a section of road, clearing out the obstructions
2. Defend a building from a zombie siege so your community can repair it, e.g. a hydro damn to supply town with electricity.
3. Repair sections of wall around the town (maybe as really difficult end game tasks) that effectively stop the zombies re-spawning so you can wipe out freaks and hordes from the town.
This would help keep your motivations to play the game and feel like you are actually making a difference.