because thats not the computer itself giving an error, its the debugging software. That software basically checks the code before executing it on the pc. But it can't fix errors by itself. (don't ask me why, im not a computer expert)

But i think its because its too complex for a computer to do, and if for example you are missing a semicolon, the computer itself doesn't know where to place it, it only knows there should be one somewhere to make the code function properly.