Compared to calling version 2 of the API with a large page size, the list of sites in v1 is getting truncated after Salesforce Meta.
From the API 1.1 docs:
Presumably, Salesforce was the last Stack Exchange site created when API 1.0/1.1 was still active, but newer sites are not getting their API endpoints created.
The original announcement on StackApps regarding the deprecation of API 1.x can be found here. (Oddly enough, it looks like Libraries was supposed to be the last site created with an API 1.0 endpoint, but the deadline was apparently extended).