It simply happened that Schroeder sought out the Pink Floyd (who knew nothing about him, after all, it was their debut) and offered them six hundred pounds each for a week of work in Paris. The broke Floyd jumped at the chance "... and we galloped happily and at full speed into the studio, throwing ourselves into it..." as David Gilmour later said. This is reported in dozens of books and biographies about the Pink Floyd... it's easy to find information; no "beginning of interest in Cinema" as you superficially claim.
Then Antonioni sought them out (having seen them on stage in London and being impressed by "Careful With That Axe, Eugene") and in turn hired them for "Zabriskie Point" practically to recreate it just like that, and not much else. Then Schroeder came back and re-hired them for the soundtrack of "La Vallèe". End (or rather, from there we jump two decades ahead to "The Wall").
You are right about "Cirrus Minor": it is splendid, a masterpiece. Especially Wright's performance. But also the "borrowings" from the remarkable sound effects tape of Abbey Road is sublime, and there must have been the involvement of Mason and/or Waters, the two "architects". No external "pushes" on "Nile Song" or anything else on the album: the Floyd were given a free hand by the director, and after all, they self-produced on this occasion (for the first time).
And I'll stop here. You say you read a lot... it seems like a lie. You really enjoy writing... great, it’s either one of two things:
1) Simply describe your feelings... the effects of the music on you... the moments that touch you the most, excite you, or conversely bore or irritate you, without going into specifics, context, technique, or historical framework. This site is full of reviews that say nothing about an album, about how and why it was made, about how it sounds, about what the lyrics say... but they read wonderfully because they are small gems of the Italian language, of life stories, of enthusiasm.
2) Provide data, facts, and situations about the work, but at this point, you need to be knowledgeable; otherwise, you’ll get commenters like me who will critique everything and conclude that you definitely often wrote things about yourself, describing events and situations quite different from what is historically set down, black on white.
Of course, there is also a third way (which I'm almost certain you will continue to favor): writing a bunch of random things as they come, right or wrong, for the sacred and banal pleasure of seeing yourself immortalized on a nice website of music enthusiasts (accompanied by idiots, layabouts, and trolls as in any respectable site).