People who wish to live in neighborhoods with low crime often NIMBY off any attempts to add public transit options specifically to keep out the riffraff.

  Marin County is home to over 252,000 residents, yet it is without a BART station. If you search
  web content to find out why that is the case, you will not find a lot. There is minimal information 
  explaining why the BART doesn't connect from Marin to San Francisco and even less explaining why it 
  doesn't connect from the East Bay to Marin.

  Marin funded a large portion of the project when BART was being planned in the 1950s. But "concerns"
  over whether or not the Golden Gate Bridge could support BART suddenly arose. After San Mateo pulled
  out of the plan, Marin's participation fell through as well.

  It is not unfair to speculate that socio-economic discrepancies might have something to do with this 
  lack of transit connection. After all, Marin is the county where wealthy residents stopped George Lucas 
  from building affordable housing on his land. The median household income there is almost $84,000, more 
  than $15,000 more than San Francisco and more than twice as much as Oakland.

  A similar situation in Dayton, Ohio arose where wealthy suburbanites tried to stop the local transit 
  authority from building three new bus stops near major employment centers.[1]