Actually, it kinda did, but it didn't stick. Both ST:TMP and TWOK, as discussed, were the kind of soft reboot that implicitly changed or ignored things without making it overt. TMP changed the look of everything and left it to us to rationalize the changes as the result of time passing, or just asked us to pretend it had always looked that way (as with the Klingons). TWOK's makers intended to quietly ignore TMP and start fresh, albeit reusing the same sets etc. because they were on a budget; and it also quietly retconned details of "Space Seed" to suit its purposes, just as Harve Bennett's earlier The Six Million Dollar Man had retconned details of the pilot movies and earlier episodes from time to time, because continuity wasn't taken too seriously back then. TNG was also a soft reboot of sorts, since Roddenberry considered a lot of prior Trek apocryphal by that point. It rarely offered any overt contradictions to TOS or the movies, but in the early seasons, TNG mostly stayed as far away from TOS characters, species, and continuity as it could.
Basically, what we had were several different versions of Star Trek with enough differences in style and detail that it was unclear whether they were really representing the same version of the universe. And had things gone on in that vein, had Roddenberry remained in charge and kept operating under that model, TNG might have ended up making a cleaner break with TOS and the movies.
But what happened later was that the franchise was joined by new producers and staffers who were big fans of the original series and who played up the ties to it that Roddenberry had tried to play down. So we got stories like "Relics" and Generations and "Blood Oath" and "Trials and Tribble-ations" and the like, firmly tying the old and new together as parts of a single whole. True, that's what most fans had always assumed it to be, but it wasn't quite what the actual creators of the movies and TNG necessarily had in mind. And if things had gone differently, if that early ambiguity had been resolved in the other direction, we'd now be talking about Trek's long history of reinventing its universe rather than its long history of having a consistent universe. A lot of that perception of consistency was only made solid after the fact, once the fans of first-generation Trek started writing and producing second-generation Trek and bringing their nostalgia to bear.
You see the same thing in other fictional franchises. For instance, Godzilla has rebooted its continuity many times, but the first reboot pretty much repudiated the lighter tone of the earlier sequels and ignored them altogether, but some of the later reboots actually reincorporated bits of the original continuity into their backstories. Then you have Batman comics and screen adaptations aggressively getting as far from the tone of the '66 sitcom as possible in the '70s through the '90s, but now embracing its tone in things like Batman: The Brave and the Bold or reviving it outright in the Batman '66 comic and the upcoming animated DVD movie Return of the Caped Crusaders. The first wave of revivals tend to react against the original and try to stand apart as something different, but then the next wave reacts against that reaction and embraces the original more fully. It's just that in the case of Star Trek, it's been in continuous enough production that those waves blended together into what appeared to be a single whole.