It appears, to me, that you do not understand the roles that the various pieces of software perform.
If you have an stl file that defines a volume, and a 3D printer, you can't just "print an object".
The printer head can move in the X direction. The printer head can move in the Y direction. The printer's extruder can extrude, or not, material. The extruder may heat the material. The print platform can move up or down. Each of the motions is controlled by a G statement. Heating, extruding, etc. is controlled by an M statement.
So, where do the M and G codes come from? Some software needs to understand the orientation and scale of the stl file, and the properties of the printer, so that it can create slices and output the M and G codes necessary to process each layer of the stl file, so that the end result is a "printed" 3D object.
Slicing is not terribly difficult, since the stl file contains a collection of triangles that define the outside of the solid. Intersecting a plane and all the triangles creates a bunch of line segments that define the outline of the slice.
The next step is to organize the line segments in order, defining an outer boundary and one or more inner boundaries.
Next, the software needs to determine how to move the head back and forth over the slice, starting and stopping extruding where the path intersects the boundaries. Parallel paths, at the required spacing, are needed, to cover the entire boundary. Now, clearly, sometimes the head needs to be moving one direction, and sometimes it needs to be moving in the other direction. Minimizing wasted motion is a non-trivial task.
Between slices, obviously the platform needs to move.
The collection of M and G codes is what is actually sent to the printer, where the printer then decides how many steps, of which stepper motor, are needed to make the head or platform or extruder do what is necessary.
What is NOT clear is what part of the process you think is too complicated, and needs simplification. It is also not clear what simplification is possible.
You sound like someone trying to understand how a TV works, saying "its too complicated; it should be simpler". Life doesn't happen that way.