Alright let's play your game... where's the tangible benefit of a Cervelo/BMC/Colnago/Pinarello over a Trek?

That's one step too far for resale... once you get into bikes of that price tier, good luck selling them used. People who have $5k to spend on a bike don't want a used one.

Edit:

Let's look at the Trek Emonda SL8 and the Colnago CX Zero Evo. Both "Dura Ace" models

Nearly the same except the Colnago has an Ultegra cassette instead of the Dura Ace one on the Trek, a $25 handlebar instead of the $100 one on the Trek. The Colnago has a $700 wheelset vs a $500 one on the Trek. So... $200 less in cassette and handlebar but $200 more in wheels, so about the same.

Yet the Colnago costs about $2500 more. You're paying for the name/frame.

That's just the first example I looked at.