Part of the issue is perhaps that DL has generally not done bump-up's since the advent of rollover MQM's. The issue is what happens to the rollover MQM's. Should you get to keep them as well if they bump you up? If someone meets the 60 segment Gold requirement and flies 40K miles they will get zero rollover MQM's. Why should someone didn't meet the segment requirement and flew the same 40K miles get both bumped to Gold and 15K rollover MQM's to boot? Maybe they are willing to make that trade-off, but I bet a lot won't consider that fact and would get mad if DL took their rollover away after bumping them.