Is this goosegrass?
Looks like it might be.
Here is a link that might be useful: Goose grass
Not sure what it is, but it's not a broad leaf weed, but a grass of some kind. Herbicides are labeled according to the plant group on which they are most effective......the monocots (grassy weeds) or dicots (broad leaf weeds). Eve though your weed has a wide blade, it is still a monocot.
I'm just reminding you of the correct terminology in the event you want to do more research or if you are considering the use of herbicides.
Well, that probably explains why the herbicide I used didn't work. Thanks much!