Epiphytic orchids in nature are found growing with their roots exposed to the various elements. They are fertilized by bird droppings and washed by the rain. The old bark is stripped off and replaced with new bark and they are in a symbiotic relationship with various other living organisms in their environment. In effect, they grow best in a dynamic environment compared to the static environment in a pot. Beyond 2-3 years, this static environment in the pot can become intolerable to the plant due to the buildup of toxic fertilizer residue, extremes in pH, decaying roots as well as decaying soggy media. This can only be set right by repotting.