Why can I sometimes not preview a resource?

Category: Site
On the data catalog site, files in specific formats (for example, HTML, CSV, and XLS) can be previewed.
Note that even a file in a format that can be previewed is sometimes unable to be previewed, such as when the file is prohibited from being previewed by its source. If you cannot preview a file, directly view the file by clicking the download button or by entering the URL.