That was determined to result from UA’s historic over reliance on regional flying, not too many premium seats. Additionally, DL has more fortress hubs with huge pricing power, along with those hubs having very low CPEs.

With UA’s significant upgauging, the profit gap was been reduced significantly and eliminated in some metrics.

If DL didn’t see a benefit in narrowing the difference in premium cabin size, they wouldn’t increase the size of those cabins.