Why is ENT rarely used for electrical wiring?
I am not an electrician, but as I'm currently in the middle of some renovations myself, I was curious and did some searching.  I came across "Mike Holt’s Illustrated Guide to 101 Essential NEC Rules" (that's chapter 3 in PDF form), which, in article 362, it explains that it can NOT be used for wiring systems over 600V.  To me, that appears to be saying that it is fine for 120/240V.  The main concerns appear to be leaving the conduit exposed, particularly to sunlight, as UV can cause it to become brittle.  I also came across a forum post discussing using ENT for 120V, and they were discussing how many wires you could run in a specific size of conduit, so it appears that it's done.  Given that it meets NEC code, I can't come up with a good reason why specific localities might forbid it, other than possibly politics.