It's the absurd fetishism of its likely impact as some unprecedented game changer.
It is entirely in line with what mainstream economists tell us about doing FTAs with distant lands.
Nice, and usually of real benefit to a few sectors, but never game changing for the economy. Ever.
However, as other trade justifications for Brexit have fallen away, the US FTA has had to carry the full weight of delivering sunlit uplands.
It can't and won't.