I don't really see it as logical problem as DL neither allows SDC/SDS, nor Preferred seating access for elites on BE fares (both are elite benefits). It comes down to policy and how painful do you want to make your BE fares so that elites will avoid them vs. possibly alienating them too much that they jump ship. DL BE fares weren't nearly as restrictive as they are now when they were initially introduced. I suspect DL saw few elites were buying them and that they didn't see much of a risk in changes. I would guess bigger issue for DL is competing for non-elites now that DL BE fares earn no redeemable miles at all (assuming few elites were still buying them, the no status earning dollars is probably not so much of a big deal).