How does the Army determine which JKO courses are worth promotion points?

The age-old question, "why would the Army give me points for learning something that is not my MOS or duty position"?
It has always been that way, even back when correspondence courses were yellow books that arrived in the mail, and you had to mail back the completed tests.
The Army has always been a learning institution, and while they have never come right out and said it, I suspect the idea is that "any learning is better than no learning", and I suspect they understand that some duty positions lend themselves to more resident courses, some commands lend themselves to more awards, not every Soldier is cut out to complete a college degree, but distance learning is the great equalizer; a level playing field where any Soldier with a little motivation can complete enough skill level 10 training on DL to max out their DL points.
Just my own guess.

SGT (Join to see) full courses will always be worth promotion points, not sure where you are seeing that some are not worth points. Sub courses are not worth points. It might be that some courses do not sync with ATRRS or that have rank or resident requirements.

AR 600-8-19 indicates, "one promotion point for each 5 credit hours".

I always recommend that Soldiers joining up for SGT and SSG max their DL points by taking courses that expand their expertise their MOS, then Branch, then other interests. Medical is one of the easiest to do that in all the OLMS systems.

If you look for "easy" points, are you really developing yourself as an SME in your MOS? That stands out in later boards.