heavier, harder to lay, harder to maneuver on job sites, (can't imagine it'd be too easy to throw a 20' stick of 8" HDPE over your shoulder and walk away with it like you can PVC. in open excavations, on gravity sewer, it's not standard to the industry. everybody in the sewer biz has bins full of pvc fittings, i'd have to drive 100 miles to get HDPE fittings.
unless you're running large excavators, 20' lay lengths are a miserable son of a *****. most 22 ton machines are not comfortable handling/pulling 24' boxes. do you fuse the crap in the ditch or up on top and attempt to get it on alignment, on grade, once shoved in the hole?
i can see where it's a great product in pipe bursting jobs...otherwise, looks like an awful lot of extra work to me.