...The movies happened because Phase 2 didn't work out but the appetite for the old crew was still there. ...
Yeah, Phase II was scrapped in favor of TMP largely because of the success of Star Wars. Suddenly, every movie company wanted their own Star Wars-esque movie:
Well, that oversimplifies a complicated history. For those here who may not know the details of
Star Trek sausage making:
Paramount wanted a ST movie before
Star Wars, and commissioned treatments and scripts, finally resulting in Phil Kaufman's
Star Trek—The Motion Picture (nee
Planet of the Titans) in development for about 9 months, but pulled the plug just weeks before
Star Wars' release, because they:
a) had rejected the Scott-Bryant script in March of '77
b) they didn't like Kaufman's first treatment for a suggested revision
c) there was a shake up in the studio management, which tends to purge works in progress by the previous regime, and
d) they feared Star Wars would steal their thunder.
So
Star Trek II (nee
Star Trek Phase II) was hatched because Paramount wanted to start their own network, and they saw the
Star Trek phenomenon as a great way to capitalize on one of their properties to launch said network with a built-in audience. But
STII was doomed when Gulf+Western's Charlie Bluhdorn nixed the investments necessary when he concluded that the numbers weren't there, stopping Barry Diller from launching this 4th network (which Diller finally did a decade later with Fox).
Finally, Paramount had already sunk a bunch of money into the
STII project, with sets nearly completed, etc., and since
Close Encounters proved that
Star Wars wasn't a fluke, and that there WAS an audience for sci-fi, they in desperation grabbed the pilot script for
STII and turned it into
ST:TMP in order to a) recoup the costs of the aborted previous projects and b) finally do what they originally set out to do: make a
Star Trek movie.
Mmm. Sausage.