When you want to build games for many platforms at once, dealing with platform-specific rendering, sound, and input code just becomes tiring. Having an engine at the base gives you these for free (or at a cost, with Unity).
A game engine is much more - it includes systems like physics, game object representations (like unity's sort-of-ECS), save/load, animations etc.
using game engine's builtins for the things you don't want to abstract yourself makes complete sense, keep the game to "game logic"