The UIs were part of Fishworks which became the ZFS Storage Appliance. A more fair question would be, why hasn't your storage appliance vendor (like Pure Storage, EMC or whatever) implemented the UIs (and maybe they have?).

As others point out dynamic tracing facilities should be there with bcc but to be honest you shouldn't even need dynamic tracing to create those graphs, just disk I/O queues, service time and throughput. I know how to get that easily on FreeBSD from libgeom(3), I'm sure it's not too hard on Linux either in one of the pseudo-filesystems.

[libgeom(3)] https://www.freebsd.org/cgi/man.cgi?query=libgeom&sektion=3

99% sure it's this: https://docs.oracle.com/cd/E22471_01/html/821-0782/analytics...

There's this library with rudimentary histograms:

https://github.com/iovisor/bcc