When im sound designing I miss the option to load full racks without having to send to a group before I can add the chain.
If I add a chain on any given channel, the inserts will be over-written by the chain preset…
Think Blue Cat PatchWork and Soundtoys Effect Rack.
Normally that’s how presets work… 
you can use any rack you want, do we really need a Steinberg FX rack? maybe…
I know how a preset works
But if you have done some EQ, compressing, whatever that you like, and you want to add a certain chain it will overwrite the work you’ve already done.
It works like a charm in Ableton although I know its not a similar DAW and can’t be compared 100%.
And to you question if we need a Steinberg FX Rack: YES, think so!
And to answer WHY: YES, I have PatchWork from Blue Cat and it is buggy as hell. I think that if Steinberg chose to make one it would be a “feature” in the Cubase Engine and not a 3rd party plugin.