I don’t always.
but have. Most of my deck building was for someone else.
Too often I’ve seen what you just said. 15k in synthetic decking over tired old framing trying to save 2k.
Just silly. But, if wanting longevity as long as possible, there is a science to avoiding wood/wood contacts as much as possible.
Just like for years it was “ get it right, get it tight”
Now it’s all about rain screens, air flow, even on post base trim wrappings.
but what’s not discussed is keeping those areas from Becoming jam packed with organic debris and still harboring moisture for prolonged periods of time.
even just painting every edge and yes, adding copper green to every cut will increase life span.
but if you frame and build it all, then have Joe blow paint on the undercarriage only hitting what’s visible, that in time could trap things within the wood and allow harm that’s harder to notice go about over time.
Metal is great, long as not to avoid rust. Longest lasting is stone, long as done right it can be earthquake proof as needed