"Drawing bitmaps" with SDL or OpenGL is a trivial part of developing a 2D engine.
Calling SDL/SFML for "other stuff" is, again, a tiny part and it is in no way offloading "the other crap" (as you call it).
I assume you are biased because you have only coded toy examples. When you start anything remotely complex, you have to do way more things than just "drawing bitmaps".
As for Factorio, it is actually a very complex and fast simulation. Downplaying engine devs as "rendering and other crap" is derogatory to say the least.
Calling SDL/SFML for "other stuff" is, again, a tiny part and it is in no way offloading "the other crap" (as you call it).
I assume you are biased because you have only coded toy examples. When you start anything remotely complex, you have to do way more things than just "drawing bitmaps".
As for Factorio, it is actually a very complex and fast simulation. Downplaying engine devs as "rendering and other crap" is derogatory to say the least.