Having said that, C# string interpolation is not user-configurable, and you cannot realistically use it to generate, say, 300 lines of highly sophisticated text that is a subject to frequent modifications during product development.

One of the popular tasks for a larger scale templating is email generation. Text templates, HTML templates, for signup, for email confirmation, for password reset, for subscription renewal, for ... you name it. As you can see, it quickly goes wild. Not sure one would prefer string.Format() or C# string interpolation to do all of that.