I wonder if the quality of pressure treating has decreased, at least for what is sold at the box store. I had a low 10x10 deck for the dogs not in contact with the ground - PT deck boards rotted in places enough to stick my foot through. Rebuild - the same thing happened after about 8 years. Rebuilt it from scratch with Trex.
I also had a small deck on a slope 3-4' above the (well drained) ground. Not only did the PT deck boards rot through after about 10 years but the beams and joists did too in places. The only thing that didn't rot was the posts in the ground. I replaced the entire thing, decking with trex this time.
JKJ