Let's put it in different terms: Scarcity.
The odds of finding a consistent 10 WAR player are pretty astronomical. You could replace him with say 3 3-WAR players but wouldn't it be best to keep your 10-WAR player and attempt to acquire or fill in positions around him with average to above average players (0-2 WAR players who are not nearly as scarce as even a 3-WAR player and can be found readily throughout the league)?
The other problem is now you have to pay three 3-WAR players versus just the one. Of course long-term that actually might turn out to be more affordable if you have to offer extensions to all of them (the 10-WAR player will have a huge contract obviously).
To me Trout is the rarest of all diamonds. He is irreplaceable and that just makes his value so high that I don't think any team could really provide enough trade value in return for him, making the conversation sort of moot from my perspective, at least right now.
Finding high production players (Over 2 WAR types) is not easy and the more productive they are, the rarer they become.