It was specifically a Great Society program meant to contrast with Soviet metros and their ornate architecture. NYC and London have the issue where they were first generation systems trying to figure out what worked and what did not.
DC’s general height limits in conjunction with typical American SFH friendly zoning also do not help utilization.
That’s america in a nutshell. We can’t infringe on people’s precious individual expression and self actualization after all. That said in the DC system, expense was traded off in favor of cleanliness and lack of crowding—the stations are enormous (and very costly).