Colloquial, "understandable" is the standard here. Adherence to spoken prestige norms and written standards other there.
Here we use phonology and "speed," ignoring derivation and sociolinguistic complexity. There we use cases and orthography.
Why?
Dunno.
Is it to achieve a specific kind of ranking for some languages? Is it because it's too hard for the writer to formulate an emotionally satisfying single, coherent standard? Is it because the standard kept evolving, but the writer didn't feel like going back and revising what the finger, having written, had already moved on from?
It's fine to dismiss the FSI standard, and many do, esp. when it comes to applications that the FSI standards were never meant to cover (which is, of course, rather an important--some would say crucial or even essential--limitation). But at least the FSI standard is consistent and coherent, can actually qualify as a standard that can find application even outside its intended setting, and works fairly well in the setting in which and for which it was derived--training adult, college-educated foreign-service and military personnel in classroom setting for diplomatic and military missions.
Personally, Polish wasn't all that hard to pick up. There's a lot of case syncretism that keeps there from being 7 genders in practice. (It's like a claim I know of that Russian doesn't have 6 cases, but 8, because it also has a vocative and it has two locatives; and it doesn't have three genders, but also animate/inanimate for all three, plus a slurry of other things. Applied to Polish ... that would be a nightmare. Then again, all that "gender" stuff is just one form of noun class marking, and there are languages with scores of noun classes ... and therefore scores of "genders."