FC content is locked behind letting people who aren't even in the FC in on it for no purpose but standing there and looking pretty. Any argument that involves this being FC content and thus is group content falls short in light of this because it's likely not even your FC helping you out.
The thing is they shouldn't lock this behind only FC members because not only would this still be hella easy to get around (50k Gil, join my FC for an airship project, leave right after...), but what if you're the one single crafter in the FC? Oh so 3 other FC members unlocked craters just for this and never level the classes again. This is another way of getting around whatever the original intent was and is just a hassle for everyone involved. I feel like any change to this will ultimately make the content even less accessible than it already is (FC-less people, people who don't know many other crafters, etc). I can somehow get behind it being FC content at least on the lore level (you may be the WoL but they can't very well give individuals permission to operate airships. Now, FCs with standing with the GCs, on the other hand...), but this specific requirement is pointless.