Because some of us don't really want to read the same thing again and again with slight variations?
....even if, admittedly, that's what a lot of superhero comics can boil down to.
The issue is how "slight" those variations are. If it's significant, than I may be interested in it as a fresh take on something I enjoyed in the past. But just replacing a plague with a giant tentacle monster that turns people into infected/Crossed/28 Days Later....it just isn't enough. Not for me anyway.
Regardless, it's not just that it reminded me a lot of Sweet Tooth....but also that I thought the writing/scripting of Sweet Tooth was miles ahead of this. This first issue was decent. Sweet Tooth's first issue was downright amazing.