Why are some adjectives placed after a noun?

Solution 1:

I'm not sure these are terribly good examples, but in general, you can get the pattern of "noun (Y)" + "restricting/modifying noun (X)" to mean [X of Y] and to give a suggestion that other nouns of the same category as that restricting/modifying noun would also apply.

For example, a company named "Smithson America" implies that there might be other companies called "Smithson France", "Smithson Mexico" etc.

In any case, I probably wouldn't analyse either of the words as an adjective.

Solution 2:

These are not adjectives placed after a noun. These are all proper names, and hence pure nouns.

If your question is why these entities would choose names like "Revenue Canada" rather than "Canada Revenue", it's largely because there's an implied "of" or "for" between the two words. There are also plenty of entities with names the other way, such as Canada Post and New York Life.