Fabric API is supposed to be modular. This means that mod devs should be able to pick and choose which Fabric API modules to depend on in their mods, both in the development environment and in production.
Fabric API is also supposed to be just another mod. Fabric API should not have special support in Fabric tooling, nor should it be a required install for players. Basically, Fabric API is simply a collection of mostly independent modules that happen to be maintained by the same organization that maintains Fabric tooling.
The fabric example mod contains a hard dependency on the entire Fabric API. Since most mod devs do not remove this dependency, most players have to download an additional mod (Fabric API) in order to play a Fabric mod, which many players do not expect. This means mod devs often assume that players have installed Fabric API in the production evnironment.