It may be because this discussion was initiated back in Jan. 2016 for the AxeFxII. Check it out:
https://forum.fractalaudio.com/threads/wishlist-bass-amps-and-effects.109177/
Back then, the idea of a Sunn and an Ampeg porta-flex were being floated as new additions for bassists. Fell off the map, never happened. The Darkglass B7k did happen, as well as a re-worked SVT, which is a good thing...but...how many YEARS of nothing new.
Most bassists who have a number of years of gigging under their belt will recognize most of these ICONIC bass amps - many were widely popular at one time or another (and some still are):
Ampeg B-15/Portaflex (still waiting)
Acoustic 360
Gallien-Kreuger 400/800RB
SWR RedHead; Studio 220
Marshall Super Bass
MarkBass Little Mark III
Trace Elliot AH350X
Sunn Coliseum; Sunn Beta Bass
Eden World Tour WT800
Hartke HA Series (3500)
Aguilar Tonehammer
Pick any 4 of those amps paired with IRs of companion bass cabinets and tell me that wouldn't make a lot of people happy.
Not to mention the very popular: Tech21 SansAmp BDDI (or one of its various flavors).
IMO, the bone of contention has never been whether you can emulate or coax similar sounds to these amps out of the AxeFx, but rather, that it would be nice to have models of these amps available in the box...no hunt-and-peck home brewing or buying 3rd party add-ons. Put them in the box. I don't think anyone would question the bona fides of the AxeFx, but certainly bassists get little more than a rare bone thrown their way. I'm guessing that bass stuff isn't so profitable to warrant development, and really doesn't float the boat of the prime movers at FAS. Oh well. So be it. Surprise me one day. TTY about this in another 6 months or so.