Count me in among those who wonder why Andrew, Camden and Vincent didn't take part in the ISP Points Challenge, especially Andrew. Vincent and Camden even skated at a recent Challenger event, maybe that suffices for USFS as a first look at their programs? (although Camden withdrew after the short, but that was a month ago, so he had some extra time to work on his programs)
And then there's also the prize money at ISP, and all of them have a shot at potentially placing in the top 3, at least Vincent does. Wondering if there's maybe an injury keeping at least one of them from competing.
(I realise they still have a second chance to participate, but why not increase your chances by getting two tries?) ...
Obviously none of us knows why these three did not compete in the first round of the ISP Points Challenge.
I myself will avoid speculation as to why -- except to make a very general comment that different skaters could feel differently about what competition schedules will work best for them as individuals.
Meanwhile, inaccuracies in your first paragraph are begging for clarification, especially with respect to Camden:
There were two in-person competitions in Colorado this summer:
Cup of Colorado, Aug 14-16
Colorado Springs Invitational, Sep 11-13
Neither of them had combined events. In other words, it was possible to enter SP only; FS only; or both SP and FS.
(And neither was a Challenger event.)
Camden competed in both SP and FS of Colorado Springs Invitational, which was only two weeks ago (and was within only a few days of the mandatory dates for recording programs for the first round of ISP Points Challenge).
Camden competed also in SP of Cup of Colorado. IIRC, he never was an entry in the FS (in other words, I do not think he was a FS withdrawal, because he was not an FS entry in the first place).
(And FWIW, he competed in the virtual Peggy Fleming Trophy as well.)
Mini-update re Ryan Dunk (who also is eligible for ISP Points Challenge, but did not take part in first round):
FWIW, his SP score at Boston Open would have ranked sixth in ISP P.C. (With Naumov's ISP score almost equal to Dunk's.)
Naumov and Altieri withdrew from the Boston SP (won by Bychenko).
FS is tonight. As of now, the original start order remains: Dunk, Naumov, Jun Hong Chen, Altieri.