Another way to think of this is "the JSON Document object is told about all types of includes it should expect, so if we fail to parse any of the includes, a problem has occurred."
A potential reason for wanting to be able to ignore this invariant and succeed parsing anyway is that you anticipate other entity types getting included in a response in the future but do not yet know what they will look like or have a strategy for taking advantage of them on the clientside.
Another way to think of this is "the JSON Document object is told about all types of includes it should expect, so if we fail to parse any of the includes, a problem has occurred."
A potential reason for wanting to be able to ignore this invariant and succeed parsing anyway is that you anticipate other entity types getting included in a response in the future but do not yet know what they will look like or have a strategy for taking advantage of them on the clientside.