Being a fan of the TNE, although I do appreciate that GDW did occasionally get carried away with the weirdness, much of it made sense (to me anyway).
Heh heh, if you ask me GDW didn't go extreme enough with the weirdness. They had fertile ground to get REALLY weird in great ways, but I think GDW was going too far down the simulationist road to really understand it (though the Breeds in
Virus Fleets was a sort of stab at it).
It has a lot to do with timespans of things. It's a problem that pops up quite a few times in TNE. I'm pretty sure (but not 100%) that Nilsen explained it once that there's a constraint involved - essentially they wanted to the pyramid scheme of the RC to give an impetus to expansion; that is, GDW wanted the idea that the RC felt this righteous anger that the TEDs (presumably) that were holding the remnant technology were misusing it while they back home didn't have enough of it.
The other constraint, of course, is that GDW wanted these totally different societies popping up all over the former Imperium to make things unique, so the universe isn't full of a bunch of same-y societies (a common criticism of the OTU, but inevitable given the size of the Imperium setting). So you have something where you have these hunter-gatherer societies or the universe littered with nations that are like Europe in the 1800s or America in the 1950s tech-wise; this is of course reinforced by the chronic problem of Traveller - bad art. So you have tall ships and the Australian Empire in PoT sailing around with Tall Ships (again, the evolution of tall ships is pretty much of the ultimate expression of the wood and cloth era ship and represented specialized shipbuilding knowledge that'd take hundreds of years to re-develop unless they had some sort of technical manuals explaining it and then were promptly lost as more effective technologies came along - I refuse to believe a society can drop to TL0 then rebuild to having Tall Ships on their own, and if they have technical manuals wouldn't they be higher TL?). Another picture and some guy on a WW2 tech level destroyer right down to the Jack-In-The-Box sailor hat.
(There's a few other constraints, like GDW not wanting the universe to become "Us vs. the AIs" and so on, more design decisions and opportunities squandered but that's my opinion.)
To get some sort of balance between the two, the writers basically decided to compromise, which resulted in a situation where canonically only 70 years have passed since the Fall of the Imperium (1130) and the New Era (1200). It's ... not enough time. They tried to write it away, saying that the elimination of medical care
and the fact that the "Fall" of the Imperium had been happening even before 1130, probably around 1120 in a lot of places but it's not enough time.
* It flies against certain canon things in the setting. Like the fact that Vilani medical science is supposed to be behind that of the Terrans (for whatever reason, don't look behind the curtain, Dorothy) yet
Vilani naturally live longer than Terrans. While 70 years might reduce human population who remember the pre-Fall to a small number of aged invalids, 70 years isn't enough to eliminate a sufficient portion of the Vilani population, the longest lived of whom iirc can live well past the century mark.
* Canonically, the Virus is relatively self-destructive and most strains burn themselves out pretty quickly. While the chains of technology are fragile, all knowledge may be stored digitally, and a lot (if not most) people will be useless and die in droves it still seems a bit unlikely that civilization would completely fall people would be reduced to TL0 hunter-gatherers using stone implements. People would know that humanity had done this before, and there's a sufficient number of people who have an interest in these things that I think rebuilding would occur much faster. In addition, a lot of devices, even if they contain a Virus "egg" are simply incapable actually turning murderously against their users. I suspect a lot of basic tools would be of this sort - tools that could be used to make newer, lower-tech tools to sustain civilization even as the higher-tech ones wear one. There's a link missing to keep humanity down for so long - my conclusion is that the Virus Fleets simply aren't active enough to keep humanity down according to the "Nilsen numbers" quoted in places like PoT; something I think the writers concluded as well as in Vampire Fleets, they started suggesting that Virus activity comes in waves.
* Even more unrealistic than the TL0 worlds (which I can see) are the weird TL1 - TL2 worlds. Seriously a world filled with middle ages knights / samurai / hoplites? I think GDW underestimates the level of knowledge that'd sustain a society like that. You'd need to find this balance where nobody knows to mass-produce enough steel for it to be useful for things besides armor and swords, yet has all this careful knowledge in things like the art of metal folding and pattern welding, knowledge that was built up over thousands of years on Earth and was lost quite quickly when other, cheaper and faster ways of producing steel were developed. It really only takes a few guys who remember something about the Bessemer Process; trip hammers, water-powered bellows, and so on are concepts, that if even people don't understand exactly how they work, if the principle is remembered, human ingenuity would eventually produce a working model by trial-and-error. This kind of knowledge isn't limited to ivory tower types who enjoy studying ancient history - there's plenty of "steel engineers" even today with dirt under their fingernails who understand such processes. There really should be an "knowledge gap" in the TNE post-collapse universe - like TL0 worlds then worlds at TL3.
My personal solution was to make the Virus a lot more active and much more "sane" (their agenda may not be easily understood to humans, but they do have one), but by curtailing Virus activity, particularly Virus Fleets, they pretty much left the door wide open for 'how does this setting even exist'?