I would have thought that there would have numerous V-wings taken out of service as the TIE was introduced. It makes sense unless every V-wing was "flown 'til blown" and even the Empire couldn't maintain the needed numbers of pilots in that case.
Maybe with the shift toward large battleships and away from fights and bombers the empire decided sending the v-wings to the bone yard was more cost effective from a political position.
I mean it's not so far fetched "eliminating the astromech requirement and hyperdrive expenses in our fighters will show a savings of 345 billion credits over the next 10 years through reductions in maintenance costs alone!"
The only trouble with that theory is that the Empire isn't real big on cutting military spending or military savings.
The Empire wants extravagance. Every military decision the Empire makes is inherently extravagant. Only the Empire would devise a battle station... housing a superweapon... with a hyperdrive! And then when they decided that the Imperial-class Star Destroyer - already the largest military vessel in the known galaxy - wasn't large enough, they built the Executor-class Super Star Destroyer that was, IIRC, something like 17 times longer than an Imperial-class Star Destroyer. And if that wasn't enough, they went and make the most bonkers starfighters in the galaxy: the TIE Defender and the Missile Boat.
The only reason the Empire would cut spending on a starfighter is so they can spend even more on something else.
And that's different from a real world government how?
Let's cut those old, but still perfectly effective and useful fighter jets so we can save $50million annually while we simultaneously aquire another fighter jet that doesn't quite replace the one we cut and costs $1billion each!
Except in the real world, they're always talking about fighting the next war: We need to be able to beat the Russians or the Chinese. The Empire only needs to worry about garrisoning worlds and suppressing insurrection. There is no power in the galaxy that can defeat the Empire or even give it a run for its money. Except, well, the Empire's own disabused populace. In fact, its most massive and extravagant weapon systems - the Death Star and Death Star II - were specifically designed to destroy civilian targets - Imperial civilian targets - not military targets. (It wasn't until the Death Star II was built that the superlaser's targeting system was redesigned to engage capital ships.)
Who does the Empire have to worry about? The Hutts? Yeah, I can totally see the crime state of the Hutt cartels (and their, what, five major systems?) being a huge threat to the most powerful state the galaxy has ever seen.
It may be possible that the Empire simply surplused their V-wings: Gave (or sold) them to colonies and colonists in Wild Space. Of course, those ships could then end up in the hands of rebels. Or the Hutts. Or Black Sun. Or pirates. Or any of another of nefarious organizations. A farming colony in Wild Space would likely be more than happy to receive free - or mostly free - V-wings (and Z-95s and ARC-170s and other obsolete craft) to defend their holdings from pirates and bandits (and any other alien weirdness that might be floating around the edges of the Unknown Regions).