Despite the nattering apologetics of the fans, Trek's near-future chronology has always been very inconsistent. TOS says that the Eugenics Wars happened from about 1992 to 1996, and expressly identifies them with World War III. Later, this was divided into two separate instances, with the Eugenics wars stuck in the '90s, and WWIII relegated to some nebulous 21st century date.
Interplanetary travel was completely unremarkable and common by the 1990s, as evidenced by the Botany Bay, and we're told that the first *MANNED* mission to Jupiter happened in 1980, however according to the "Enterprise" timeline, we still haven't been anywhere else in the solar system by the early 21st century, and we were still sending crappy little R/C rovers to Mars.
It's implied that Warp Drive was discovered in 2019 in TOS (Debatable) but it certainly had nothing to do with the Vulcans, and Zephram Cochrane is said to be from Alpha Centauri, presumably a human colony there.
Clearly Trek takes place on a timeline divergent from our own, where space exploration was fundamentally more robust, and where we didn’t simply abandon it after we went to the moon. (This seemed the obvious bet back in the day. Who’d spend all that time and money and risk getting to the moon, and then just abandon it? Who’d go that far, and not go on to Mars?) That’s fine, I don’t have a problem with that. All SF universes become alternate histories eventually. Once their earliest fictional date is passed by the real calendar, that’s it. What bugs me about Enterprise (Among the many things, really) is that they keep attempting to shoehorn ‘real’ history (Crappy R/C rovers on Mars, the ISS) in with Trek history, presumably to make the show seem more relevant. Or perhaps just because they aren’t paying attention to their own backstory. That’s happened a *lot* in Trek. This is a stupid and distracting thing to do, however, because obviously if we’re exploring in person Jupiter by 1980 (And presumably having explored Mars in person at some point prior to that), then why the heck would we need to send remote rovers or the crappy ISS? The DY-100 Botany Bay is *larger* than the ISS, and that’s just a ship, a completely unremarkable freighter. Unremarkable because there was a lot of freight traffic in space by the 1990s. Actually, probably earlier than that, since there’s nothing to indicate the ‘Bay was particularly new.
Kirk once says that TOS takes place about 200 years after 1966, elsewhere Khan says that he was a prince on earth 2 centuries earlier, which would mean that TOS takes place somewhere between 2166-2196. Split the difference, call it 2181ish, yet by the movies they'd somehow decided they were in the 23rd century.
All that is leaving aside the obvious chronological problems like the Federation being at war with the Cardassians, evidently, during the first four years of TNG, and no one ever bothered to mention it, or Q mentioning the Federation’s defeat of the Klingons in the years between TOS and TNG, which was later erased from continuity by ST:VI The Undiscovered Scooby Doo.
Part of this was that in the early days, no one gave a crap about reasonable prognostication, they were just banging stuff out to throw on the screen with precious little thought given to continuity or implications (And such as their was came entirely from DC Fontana) Of course in any case where you have a lot of different hands working in the kitchen, whenever a story is written by committee, or by people working on more than one end of history at the same time (TOS movies were still coming out when TNG was on the air) you’re going to run into these problems. Every future history runs into ‘em - Known Space, Heinlein’s Future History, Varley’s Eight Worlds, Pournelle’s Co-Dominion, you name it. There’s a whole lotta’ retconning going on.
Trek, having to burn through 22 to 44 stories a year, for *decades* has obviously run afoul of this, and ultimately you get to the point where your timeline is completely irreconcilable.
Some shows come up with ways to dodge this - SG1 is probably the cleverest at it, Dr. Who can and does reboot its history quite a bit, though given the nature of the series it still makes sense internally even after that‘s done.
So there you have it: Why Trek‘s chronology is so sloppy.