If you don’t, then low-level actions will constantly be interrupting your flow of thought and you won’t be able to see the forest for the trees.
Think about all the skills that a basketball player has to execute in parallel: they have to run around, dribble the basketball, and think about strategic plays, all at the same time.
If they had to consciously think about the mechanics of running and dribbling, they would not be able to do both at the same time, and they would not have enough brainspace to think about strategy.
It’s the same all the way up the ladder of math: from arithmetic, to algebra, to calculus, to all sorts of university-level math and beyond.
If you try to advance to the next rung on the ladder without standing stable on the previous rung, then you’re going to fall off the ladder.
And even if you get saved by grade inflation and manage to make it up a step without completely falling off, it’s the next step that will get you.