From Google Support:
Why to use page-level permissions
Page-level permissions allow you to..
Is the sentence "Why to use page-level permissions" grammatical?
English Language & Usage Stack Exchange is a question and answer site for linguists, etymologists, and serious English language enthusiasts. It only takes a minute to sign up.Sign up to join this community
It’s a headline, first of all, where some grammatical rules are different anyway. So this is not a sentence, but a noun phrase:
(This section tells you) why to use page-level permissions.
That is, it tells you why you should use them. “Why to…” and “why not to…” are very common in headings to encourage or discourage the reader, respectively. The heading could just as well be:
Reasons to use page-level permissions
As others have noted, headlines are not always full sentences. Assuming that's not the issue, it is perfectly fine to have why followed by to (as part of an infinitive verb).
Perhaps you are more familiar with "how-to" titles, or similar phrases:
Well, why to is just as valid as how to, etc.