Quick and dirty 5 minutes craft: Draw a rough shape, define the contact surfaces & load, click run, and get the optimized shape. The last step is converting the output to a printable shape and running one more simulation to double-check it is strong enough.
This particular holder is a filament spool holder designed to be loaded with up to 5.5kg of filament (1x2.5kg, 3x1kg).
More than likely the static supports used in the software were in the locations you see now,1 for spool and other’s bellow on the rail. They said “draw a rough shape” as a step, so that dictated the shape.
If the static loads were placed at even height you would end up more triangle like or more of a truss. Depends shown many iterations were used also.