According to a leaked document from Federal Communications Commission (FCC) database, dated August 1st and spotted by Androidpolice.com, Nvidia has decided to cancel the tablet "for business reasons".
The earlier rumored Shield Tablet refresh, which was spotted at FCC, packed some impressive specifications, including an 8-inch 1920x1200 resolution screen, faster Tegra X1 SoC, 3GB of RAM and 32GB of storage.
The most probable reason is the decline in tablet sales and Nvidia's focus on motor cas.
Hopefully, this doesn't mean that we won't see any more tablets or similar devices from Nvidia in future but not the new Shield Tablet.