Recent advances in genome sequencing and microbiology have been shedding new light on eczema and atopic dermatitis. The most interesting of this research has been in the area of filaggrin and a genetic mutation which occurs in some individuals (source). This mutation has been shown to increase the chance of a variety of skin and allergic disease (source).
Perhaps, seborrheic dermatitis is closely related to this gene mutation as well, and there simply has not been any research specifically on its relation yet.
The future of DNA sequencing is likely to hold many answers to seborrheic dermatitis. And hopefully, much of this research will be published in the near future.