Not unusual as many bike makers are using unbranded rims and hubs from Taiwanese suppliers. Not saying it's a bad thing, I build with some unbranded rims that are very well made, rounder than certain brand name rims and better finishing at the seams.
Your case is an issue either with poorly built wheels, or a rider that rides heavy. I sold new bikes in my shop that had issues like that, one brand in particular. Got so that truing and tensioning of the wheels was part of the assembly process which made assembly more labor intensive than it should have been for mid level bikes, but it saved costly repairs down the road.