Not every page or app needs framework. But building complex app without one would be very hard and time consuming, and your team would need to come up with ways to solve problems like architecture, code structure, routing, data management, state management, etc. So you would basically reinvent all the wheels on your own cost, and you will have a non standard solution, that would not be compatible with libraries out there (for example UI components) and neither with new devs. Before Angular and React came I was building apps with plain JS with jQuery (not a framework, just a lib) and I would never go back there.