Maybe banned because there are no back-doors
My suspicion is that Huawei kit is actually secure and there are no back-doors or spyware in it. No phoning home or anything dodgy going on at all. I strongly suspect they are banned in various countries precisely because of this. The governments on question can't spy on people using Huawei kit and thus don't want people using it. I'm more inclined to believe in Huawei's honesty over the US, Australian, UK and New Zealand governments any day.