May I ask which "personal qualities" make Kander more "relatable" and a "stronger challenger" than Galloway? Presumably the same "personal qualities" that make Jon Tester more "down-to-earth" than Kathleen Williams, Amanda Curtis, and Kim Gillan? 
Beyond being a vet (which does score a significant number of points in MO), Kander had a very strong and underreported pre-existing relationship with the Kansas City African American community, and was also decently well-known among the suburban and affluent communities already trending Dem in Clay, Platte, and Buchanan counties, as well as the portions of Kansas City north of the Missouri River (much more affluent and conservative than the city as a whole). He began with a big head start in this densely populated area that Blunt's campaign didn't realize until very late in the game.
I understand the point of this post was to point out sexism, which I agree with 100% and especially in the cases you mentioned. In this particular case, though, Kander was uniquely positioned as a challenger due to his pre-existing ties and cultivated support.
St. Joseph is growing both economically and racially, albeit much more slowly than KC's more inner suburbs. The city's mayor Bill McMurray (disclaimer: a friend of mine) is popular and has developed a following in the region, with definite potential for higher office. Buchanan has also been one of Sam Graves' weaker spots in the district, notably in 2014 despite the wave. The county has obviously moved away from Dems since 2008 and is to the right of the state but has shown signs of resistance to the state's R trend, especially for regional statewide candidates.
Buchanan County perfectly displays the state's R trend better than perhaps any other Missouri County. Buchanan County voted for Obama in 2008 while Missouri narrowly voted for McCain but it has trended so far right that it's voted to the right of the state in every election. Even Nicole Galloway only barely won it by like 2% last year even when she was winning statewide pretty easily
