'They' didn't - EA shit the bed regarding the realistic handling SMS had in place, ordered a change hance the horrible handling. Anyone remember how screwed up NFS: Shift was on release? The Xbox 360 version was nearly unplayable thanks to horrible handling cars and terrible AI while the PS3 version shipped without damage being enabled! This is what happens when the publisher orders 'eleventh hour' changes to the physics. The April Fools joke from SMS is pCARS starting with the old EA 'It's in the game' video
As you probably know, Ben Collins and Nic Hamilton are handling consultants on pCARS; I doubt SMS want to waste their time and SMS's (plus money) on getting feedback from these two and then settling for an arcade racer.
If SMS deliever on their promise of combining the best graphics (as noted this includes changing weather and time of day) with great physics and sound, a robust career and online mulitplayer then we all benefit irrespective of gaming platform. It'll mean everyone else developing racing sims will have to lift their respective efforts too to match pCARS.