Because it is designed for 50/60Hz like every other "standard" bridge rectifier so everything is specified in terms of 8.3mSec. If you want something fast, get four ultrafast recovery diodes snd make your own bridge.
Even if you measure the recovery on one gbj-1508-f, the next one might be different if you are looking for any frequency above 60Hz input.
Just out of kicks, I once measured the Trr of common 1N40xx rectifiers.
As the previous post mentioned, Trr is literally all over the place.
Use UF40xx rectifiers for your own bridge, they are ubiquitous and low cost.