You're right, you don't know...unless someone purposely changed it.
My best guess is a tired engine where the valve clearances are way out of factory spec. possibly on their way to a burn't valve, or two.
Fuel injectors are likely wasted to. Smart owners would have sold the truck before it had 200k miles when it was still worth something, instead of the huge money pit they now face. Took me too much time before selling my gen1 tundra while hoping toyota would build a new tundra model of similar size instead of building even larger. Seeing the covid epidemic coming in 2020 convinced me it was now, or never to buy a new truck, and the taco was very similar in size to my old tundra. You just gotta bite the bullet, and do it. I'd guarantee if you bought a gen3, or 4 that performs anywhere close, or better to what I have, your going to be one happy camper.
As far as tw, i'm convinced they have a number of young gen1 first time owners that aren't too bright, or very naive. It's the blind leading the blind over there. I think when they get older with more experience, most will wise up.
