There just aren't many car batteries that are at the end of their life in a vehicle. Their lifetime seems to be a lot longer than many thought early on. Other than the Leaf batteries, most EV batteries from 10 years ago are still going. Even with those the volume was low. Now that volume is increasing, it will still take 10-15 years before you start to see the current batteries available for reuse. The average age of a car on the road is around 12 years so you will start to see vehicles decommissioned and many of those will still have useful batteries but we need much larger numbers of batteries and sooner for grid-scale usage.