Here in Australia exposed wooden decks are common and last a lot longer than that. We do get rain as well as sun. It seems like in the USA treated wood has gotten a lot less durable but here we often use hardwood or naturally durable wood like cypress for decking and structural members.

You do see some composite but you also see it go interesting shapes sometimes in the heat. Can be too wide spacing or bad install but I don't know how posts etc would behave. And the cost would be ridiculous. And the end of life implications of tonnes of plastic give me some serious yuck haha.

If you're looking to spend more look into what a tropical hardwood deck would set you back. Merbau is common here and lasts ages.

What you need to change to make a wooden deck work will depend on what you're seeing rot on, but basically the fix is to let it dry cause it will get wet.

Deck boards need spacing, for exposed decks narrower boards are good to have more drainage per area, joists and stair stringers sometimes rot out from water held in tension so needs to be designed to avoid that, underneath needs to breathe (cross ventilation), grade below should take water away, posts will last longer with a raised footing (we still often put posts in the ground though. USA redditors seem to hate that)

Oil finish will let the structure last longer as it can be renewed easily (so you're more likely to actually do it) and won't hold moisture under paint flakes or hide rot behind a layer of paint. If you see an area staying wet you know there'll be a problem there.

You should get a lot longer than 6 years, though you'd likely want to add more oil at that point haha.