There is no point I was making, you are asking a question.
A question with not much sense to it, like asking why do home builders still use wood, what answer would you expect ?
The reason your Gradys sustained wood damage is either one or both of the following: the wood was not sealed properly at the factory frok birth and /or anyone installing things or maintenance into the wood wasn' done properly. End of story, no other reasons.
Don't blame wood for rotting, it's not the wood's fault.
What's the roof of your house made of? Keep it dry and it was last until forever. How long is forever? Longer and more valve than any written warranty you could ever find.
The problem for you to solve while shopping, has nothing to do with wood or non-wood construction, so don't fret over it, if you read another thread here you will see another's members experience with a nonwood transom collecting water and the well known manufacturer refused to do anything about it, like it didn't matter. Well it does matter - but no warranty coverage for water in transom.
Your situation is very readily solved by buying new and dumping before warranty runs out, that's all you need to do, the same applies for cars, trucks, etc, then it will not effect you adversily the two reasons above, both out of your control.
No wood, untreated or not will self destruct in the warranty period, hence the reason the warranty is for the duration it is offered, not a lifetime one -make sense?
And does the warranty differ if more expensive non-wood members are offered?
No you say? Well why not? The material is 2 - 3 x the cost of wood, don't you expect a longer warrany?
The nonsense about wood guaranteed for life not to rot is nonsense sales speak, because the liability is limited to handing you over a bunch of wood to settle warranty, What good is that?
ie. How you you get the rotted wood out and truckload of replacement wood sitting in your driveway into theh boat?
Old wood has to be cut out and replaced, labor is 85% of the very expensive structural grid or transom replacements.
The transom on my boat in the valve of wood is about $350 (3 sheets of 3/4 ply), so why would a transom job cost $4-5k?
Get copy of warranty and have your lawyer read, for any brand boat you intend to sign at the dotted line on. Sell in less than 5 yrs.
Good luck!