Marc Lelijveld points out that, just because the kitten covered its eyes and can’t see you don’t mean that you can’t see it:
Most of us probably know, but every now and then, I still run into cases where hiding pages in a Power BI report is used for security purposes. Although hiding pages might seem like a security feature, it is not intended to be used as one since it can be easily bypassed. Users can find hidden pages by simple URL tweaking or right-clicking on the tabs. The article provides an example of how users can use the Reports-Get Pages API to get all report pages and report sections without having to write a single line of code. The default page when publishing a report is the one that is open, even if it is hidden.
Yeah, hiding pages is really more of a convenience thing, especially if you’re making heavy use of drillthrough and other cross-page functionality.