This is one of the interesting connections on the chart. My theory (being an ex-welder as well as a dancer) is that both of these are strongly one-gender domin

This is one of the interesting connections on the chart. My theory (being an ex-welder as well as a dancer) is that both of these are strongly one-gender dominated professions - almost all my welding friends were male and almost all my dancing friends were female (in three different states no less). And for the majority of marriages up to this point in largely heterosexual historical data, you don't meet many people of the opposite gender to marry in your regular day. The one exception is when set workers (male welders) are around a stage all day where the performers (female dancers) are doing the show. So you get these relatively few places to meet a potential mate that turn up in funny combos.