Delta's trip mix is horrible. In order to hold day trips on the 737 as an FO in Atlanta you need to probably be top 5% and those guys are all like 20 years seniority or so. There are ways to drop your schedule and pick up broken up day trips, but that takes work and doesn't always work out. Somewhere like LAX there are even fewer day trips and you rarely see anyone with an entire line of them. It's not like an LCC or even a regional where once you get some decent seniority you can do day trips. Delta likes to build 4-5 day trips as much as they can.