I think the real answer is a lot simpler than some people think.
Delta is still charging a premium for business travelers who want the flexibility of the coach fare and is quite happy to profit from those who cannot book "first class" fares no matter what the price. If employers are too inflexible to adjust to this reality, then they will just have to accept losing money. Maybe if companies start adjusting to the new travel realities then Delta will back off on such extreme price differences.
I believe the primary goal here is to extract more revenue from leisure flyers who don't need the flexibility that a Y/B/M/F fare gives but are willing to pay a slight premium to fly First Class.