Why is there no sign of it even existing. There's no parking or anything where google maps takes you

There is also a sign near a bench for Gwinnett county transit bus that's in front of a furniture store on buford drive. There's also paths behind the furniture store on the backside of that strip mall...

There is an entrance by the Salons at JC where there is a sign (park in the lot by JC and walk down to the sidewalk next to the highway and you should see it)

Kate Tilton's answer was spot on! I found the entrance to the trail at the very bottom of the exit from the 85S on Buford Rd.