Before updating a cudnn version (or any other 3rd party library) we are usually running it for a couple of weeks in the nightlies to get visibility into potential issues.
In the 1.9.0 release we were working on fixing the library split issue, the missing cutlass/xmma kernels etc.
While cudnn8.2.1 is already released, the risk was too high to fix the outstanding bugs and update cudnn without the visibility of the nightlies, which is why it’s delayed.