Rationale is pretty simple. Delta think limiting upgrades and selling the space will enhance revenue and profit. There are many folks on this website who disagree and some who agree. Time will tell.

Personally I think we will see more FCM on those route, with offers of $149 one way upgrades. What most folks don't think about (on this website) is there is more value to Delta in the $149 upgrade than $149. They are in fact attracting a high fare economy flyer (someone on a M or B fare) to buy the ticket. So say it's $1000 on AA in Coach and $1000 in coach on DL but $1149 on Delta in FC - folks will choose delta. So Delta captures, through FCM, more last minute economy flyers .

I've paid $49 to Upgrade a 5 hour transcon on Delta, but the reality was my fare was $1250. A win win and more revenue/profit to Delta.