I'm not sure how you got those improvements strung out that far from your city in that save (that part may be a bug)--the behavior that you can only build off some of them is correct, though. You're supposed to be limited to a certain radius based on the city's level.
There used to be a garden linking the buildings, but it vanished the turn prior, as reported in a separate post.
https://forums.elementalgame.com/386067
