Why are these supposed high capacity bed frames for plus size couples so unreliable?

I am a 600 lb male and my partner is a 300 lb female. We currently have a NKZ 20 inch tall king size bed frame from Amazon that has a 4000 lb weight capacity and it is already falling apart. With whole support beams cracking under basic usage. Does anyone have any guidance on how keep from having to buy a bed frame very 6 months?