Well, there are many questions about z-values. Extracting them from transactions, and signed messages, can be tedious.
To be clear the z-values aren't part of the transaction so they are not stored in the blockchain to be "extracted". They have to be computed, then the explorer has to store this additional data on top of what they are storing (that is tens of gigabytes of additional data).
I honestly don't see the utility for such a explorer though.