I think the main reason nobody uses them is that it’s hard to get a high quality burrower carapace. If there was a high quality burrower carapace with a fixed location people would be singing its praises. Burrower carapace has a small niche with tac vests where you can get 50% armor penalty with a sturdy vest, super steel sheet, black cloth, and burrower carapace. Combine it with Juggernaut, specced hit and run, and some decent quality ninja tabis and you get a tanky mobile build that can stealth effectively against anything with lower detection than a greater coil spider.