I think I can try to give and answer by comparing orange to cp_5gorge, which is the only 5cp map i can remember so far
P)
5gorge has quite large distances between the cps, so when you die it's a long way back to combat. Orange has short ways and it's easy to get back imo.
5gorge has quite many corners, making it easy to camp there. Orange makes camping really hard due to the line of sight.
It is hard to find cps on 5gorge for beginers, even while there are signs. Orange has easily recignizable cps.
And, finally Orange has a simple layout any allows really weird things because of its easy construction (such as getting on the spawn roofs).
I think these are the main reasons while orange is popular as hell.
I personally enjoy it too, but I also like quality maps made by real pros.
PS: To be honest, the new map sd_doomsday is really hard to play due to the many ways and bad navigation possibilities.