SDL OpenGL Question! 2D Engine

Hey !

I am making a 2D RPG.
So far i have written it in C++, using SDL libraries, but more and more i am finding people using SDL but then using OpenGL for the graphics part of the engine.
Why is this?
Can SDL handle an entire games graphics by itself?
Do people use OpenGL because it's easier?
I am confused why anyone would use OpenGL for a 2D graphics engine, if SDL can do this on it's own?

Thanks.

OpenGL is hardware accelerated, meaning that it's faster on most of the machines out there than SDL, which uses software for rendering. Also, SDL can't to 3D rendering natively either, without going through OpenGL.

I think as more and more people find out how simple it is to create both an OpenGL framework and DirectX framework, most choose to create their own.