For me it was some of these jobs not having heterosexual lines in both directions. "Electrical Power-Line Installers and Repairers", "Pipelayers, Plumbers, Pipefitters, and Steamfitters", and "Welding, Soldering, and Brazing Workers" don't have any female -> male lines at all if I'm reading the charts right, just male -> female and female -> female. "Miscellaneous Office Support Workers", "Receptionists and Information Clerks", and "Preschool and Kindergarten Teachers" are the reverse.
It makes sense given that gay people are more likely to be gender nonconforming and all of those jobs are gendered very strongly, but still interesting to see the extent of it.