Smells like market landscape fishing but ok. Vanilla JS + vanilla PHP....frameworks are for resumes, not for sense or pleasure...
Frameworks automate the boilerplate away so you can focus on the things that deliver business value. Clients ultimately don't care how their problem gets solved, but from your perspective you're better off spending 1 hour implementing the business logic rather than that + an extra 10 hours implementing a URL routing system, database access/management/migrations, etc.