Perhaps high school - and high school related activities - have become more time consuming. Likewise, if San Francisco parents are on average more wealthy than

Perhaps high school - and high school related activities - have become more time consuming. Likewise, if San Francisco parents are on average more wealthy than in the past, their children would be less incentivized to work for minimum wage and more incentivized to compete academically (or in related capacities) for fewer, but more fruitful, future opportunities.