This has been discussed before and there is no obvious explanation. I would guess there are two possibilities:

1. Chrysler negotiated a volume deal on the PS2s and got a great price from Michelin as the OEM tire supplier. Maybe Chrysler actually paid more for the Continental all-seasons.
2. Chrysler sought to take advantage of customers who naively thought that somehow all-season tires were naturally more expensive than high performance summer tires since they offer some capability to be driven in frozen precipitation (of course, at the expense of both dry and wet, non-frozen pavement handling).

I would lean towards #2 since many, if not most, Crossfires in northern climates had the "option." Since the vast majority of Crossfires were purchased at huge discounts, the tire price option probably didn't figure in sales prices anyway.