This is the reality of Tuesday flying in the September low-demand period. September is, by far, the worst demand period domestically in the US; and Tuesday is, by far, the worst demand day-of-week. Those two combined make for brutal flights.
Over the years airlines have gotten better about (1) flying less in September broadly, and (2) flying even less on Tuesdays in September, so I doubt the Tuesday transcon load factors are as bad as they used to be. But I'd still bet dollars-to-donuts there are a decent chunk of low (sub-60%) load factor Tuesday transcons flying around as we speak.