When you mention Risers, is this Bus Duct [Busway]?
Bus Duct / Busway will have Vertical enclosures running though the floors, and have Breakers Tapped off it at each Floor's Electrical Room.
If this is what you are referring to, then the most likely reasons for the Elevator Equipment being Piped are:
1: Elevator Equipment is in a location that's much easier to service from direct Pipe Runs,
2: Elevator Equipment incorporates a Standby Generator / UPS
3: Bus Duct feeding per floor user end equipment should be separated from the Elevator Equipment's Power Circuits and other heavy loads-such as HVAC, in order to lesson the problems of Power Quality for the Tenants.
Let us know if this makes sense!