Seattle elementary schools are weensy

So saith the Times:

Twenty-nine of Seattle's 61 elementary schools — almost half — enrolled 300 or fewer students this past school year. No other Washington school district with more than 2,000 students had that many schools that small. Many neighboring districts don't have a single elementary under 300. Some start at 400.

More surprising to me is this statistic:

One big reason Seattle has small schools is because it didn't close enough schools to keep pace when enrollment declined from about 100,000 students in the late 1960s to about 46,000 today.

A graying population? Unaffordable real estate? Industrialization? All of the above?