If its a big project you will end up with the MVC , Angular and WebAPI by default. You can not make UI in pure HTML. If you make in pure HTML you will not be able to get authentication authorization and many server side coding on UI.
Think about it you make invoice.html every body can just see it. You need to make invoice.cshtml so that it goes through MVC windows/forms/oauth authentication process. You will need razor for server side coding.