What is Dependency Injection in ASP.NET Core and why is it built-in?

Dependency Injection (DI) in ASP.NET Core is the built-in mechanism for constructing and wiring application services.

The framework provides a first-class DI container that:

• Creates and manages service lifetimes.
• Resolves dependencies for controllers, Razor Pages, middleware, and other components.
• Encourages testable, loosely coupled code.

Having DI built-in removes the need for static helpers or service locators and standardizes how dependencies are managed across the whole stack.