Instrument approaches are designed such that several divergent paths and procedures funnel into one of a few common designs. Almost every approach you fly will either be a cone of narrowing vertical and lateral guidance; or a staircase of stepdowns to a minimum altitude.
Not so with departures. Here each runway is a potential departure point, plus there might be options for a visual climb over the airport (VCOA) to a safe altitude before heading on course. There are a theoretically unlimited number of potential routes. Designers must accommodate the infinite within the constraints of terrain, overlying airspace, potential climb gradients, and available navigation aids.
