The TOS films told stories over multiple films kind of by accident, not always by design. TMP was stand alone. One and done. They never expected to make a second. When TWOK was mounted, they stayed as far away from that film as possible. TWOK was also supposed to be a stand alone and final film, but when the box office came in and Nimoy wanted back in the franchise, that's when they had to continue directly from Star Trek II. If Nimoy didn't want to come back but they went ahead with Trek II with Saavik as Spock's replacement, it would probably have been another stand alone. But nope, they had to bring Spock back. TSFS was saddled with an Empire Strikes Back kind of unresolved ending (other than actually restoring Spock), so they wrapped up those loose ends in TVH, but the main story wasn't dependent on the previous films, just the set up on Vulcan and the last 10 minutes. The bulk of the film was unrelated to Treks 2 and 3 and worked as a time travel comedy. They could have written this film anywhere in the run really. Cut a few lines here and there about Spock's memory and full death experience and you're golden.
TFF was completely stand alone. It was a fresh start with hardly any connections to past films (and even made up new stuff about the characters) and Trek 6 went out of its way to ignore it. However, TUC does build a little on prior films (David's death by Klingon, Admiral Cartwright). But it was really the only one. The rest were serialized because of the Nimoy situation and arguably, only TSFS fed directly off it's immediate predecessor. You needed to see TWOK before that. TUC picked up the main thrust of Kirk's racism from the climax of TSFS, but that could have been just another episode also with some rewriting and none of the prior films were required viewing. Out of all the sequels, I daresay TSFS was the also only one aimed squarely at the fans. The general audience was lost.
Not unfair. I see your points.
To be generous, TFF does at least make some token efforts to carry back to where TVH left off, with 1701-A being refit and relaunched, etc, and it arguably acts as a much-needed 'breather' in the arc plot that encompasses TWOK through TUC.
But yes, I conceed it may have partly been by accident... but nevertheless, the
assumption was there that you use the plot of the previous movie as a springboard in each sequel. So, TSFS continues the Genesis plotline, TVH shows our heroes returning from exile on Vulcan in their borrowed Bird-of-Prey to face the music for stealing the Enterprise, TFF launches the new Enterprise and begins steps towards some kind of peace with the Klingons, and TUC kinda cherry-picks elements from all four previous movies to tie up (the Klingon captain Klaa from TFF even reappears briefly, providing continuity threads even through the fifth movie).
Generations continues this general trend to begin with, starting aboard 1701-B feels like a nice gentle way of transitioning from Star Trek VI to Star Trek VII, but after that there's not really even any precursory attempts to carry elements or narrative forward directly from instalment to instalment.
First Contact takes place more than a year after
Generations, starts from a kind of 'Year zero' approach (which is not necessarily a bad thing, don't get me wrong, I've found it's a very easy gateway into Trek for uncommited new viewers), but the emotions chip is essentially discarded (Data can now switch it on or off) and events basically ignore anything Borg related that happened on TNG after "The Best of Both Worlds". The emotions chip is officially abandoned in
Insurrection, with barely one line to explain it's complete absence, and the plot makes no other attempts to tie back into the previous two movies.
Nemesis at least continues, broadly, the Troi/Riker arc from the previous movie, but is extremely cavalier about what other bits of continuity it accepts or rejects.
The approaches are entirely different. It is, perhaps, prudent also to remember that during the TOS period, where production overlapped, the TV production and movie production were handled by entirely different teams, whereas from the seventh movie onwards, everything Star Trek started and stopped with Rick Berman. I truly believe he had no instinct for movie production, and approached commisioning the movies as being just like selecting episodic TV scripts, not feeling a great sense of needing to 'over-arch' the TNG movies in any meaningful way.