There is no motivation for someone to teach in inner cities beyond a sense of civic duty. I live in a city with terrible (unaccredited) schools. Students in those schools are often openly hostile to teachers and faculty. Administration is often on the verge of a breakdown due to the pressure to "turn things around." Why would anyone want to teach there? I know I didn't want to.
If you think it's a travesty that talented and bright teachers want to avoid inner cities then you should do it yourself. That's what I say to anyone who brings this up. Often I will be told, "But that's where you're needed!"
"So are you," is my response.