My understanding is that the alien “blob” parasite is the reason for zombie resurrection.
The “blob” tries to control the minds of humans but is only strong enough to do so when the humans are dead. The “blob” can also make changes in the human body, which explains why mutations work. Currently it appears that the only way to figure this out inside the game is to read a bunch of content in labs (i.e book titles and computers next to turrets). In other words, this very important story element has been literally locked away in middle/late game content.
If there is supposed to be a parasite blob inside of zombies. Maybe this should manifest itself within the game. For instance, butchering a zombie might have a small chance to produce blob globs. This chance might be higher with large zombies such as a zombie hulk.
If blob monsters are actually just another manifestation of the “blob”, then what about having a small random chance for blob monsters to form when you butcher a zombie (chance could increase the closer to resurrection), or maybe sometimes instead of reviving a zombie a blob monster will be created.
My general idea is that we should relate the blobs to the zombies so that they don’t feel like completely separate ideas that have been thrown together. Thought has been put into the back story and the game should expose that.