This seems odd to me. I have been working in .Net MVC/Core and while I could write an application that is simply HTML/CSS/C#, I would think it would be insane to do so.
It takes a massive amount of resources to develop your own security, your own data access without any ORM tools, not cause memory leaks, properly disposing of resource.
I'm all about creating reliable applications, but a good framework is a great tool.