The wall mount racks that I've used aren't ideal, but they are the best fit for some projects.  These are DWR and there are knockouts in the top so the wiring doesn't need to enter from the wall behind the rack.  I dressed up the wires with Panduit finger duct:










Here's a job I'm working on right now with a pair of BGR ganged together with the cable chase between them and wiring coming in the top:











This is a single ERK with cables coming out of the wall high up and then into the top of the rack:





Problem with having the cables down low and on the floor is that the always get bunched up under the rack so you can't roll it back.  If you have access behind the rack might not be as much of an issue, but a big bundle of wires on the floor attracts dust and makes it difficult to clean.