To me the main reason is the lack of marketing from the media, the PR department of ISU, or whatever the source that help generate the public attention.
I don't think the ISU does much marketing, it's the individual federations. Other than that, agree.
The US is in a kind of negative feedback: their pairs don't win as much as singles, so don't get as much publicity, so don't attract as many skaters, so don't win as much, so don't... The same seems to be true in Japan. In Canada, all the disciplines are more equal both in terms of publicity and success.
I would expect the popularity of pairs in the US to increase if they have more success, but has that happened for ice dance? Maybe it takes a long time for the popularity to come? Or maybe it would work better for pairs because it is more similar to singles, with its big tricks.
Not having any pairs in Stars on Ice is certainly not helping pairs in the US.