 Why he wasn't canonized? It's important to bear in mind that a person is canonized not because they write wonderful books, but for a complex range of other eventualities which may or may not be there. The fact that a person isn't declared a saint or isn't added to the canon of saints doesn't mean that they're not a saint in the sense that they're a person who is very holy and so forth. The fact that we don't call him Saint Thomas the Campus doesn't in any way detract from his undoubtable sanctity.