...have such shitty public schools?

Conservative blog SoundPolitics.com has some ideas why. Of course, L.A.'s public schools also suffer from many of Seattle's problems, so the discussion's relevant down here, and all over urban America. Quoth the Sound:

All these cities are "progressive": Los Angeles, San Francisco, Seattle, and Washington, D. C. All of them have poor schools, and some of them have terrible schools. (All of them also have high housing costs.) And you can easily add a great many examples to that brief list. One can find university towns that are "progressive" and have reasonably good schools, but on the whole, in cities where "progressives" run things, the schools decline.

One commenter has an "answer" that I largely agree with.

It's all about supply and demand. It's too, too, too expensive for most middle-class parents to live and work in Seattle (or San Francisco. Or even Los Angeles). Taxes are too high, mortgages are too high, and, let's face it, the houses are small, transportation is bad, and the general cost of living is just too damn high.

Because of this, most middle-class parents rationally take themselves and their families out of the city. And that, in turn, means there are fewer students and less demand, city-wide, for high-quality schools. Why would a childless couple living on Queen Anne, a wealthy Madrona family whose kids go to Lakeside, or the single young people who crowd into Capitol Hill or Belltown give a rats-ass about the Seattle schools?

The dirty little secret ... is that as long as the people of Seattle continue to over-tax themselves, artificially inflate the cost of property with punitive land use regulations, promote high-density housing instead of family homes, maintain a too-small police force, and discourage the use of family cars, families will continue to leave the city and--no matter how much money you give to the schools--there will be no real demand for good services. And government will continue to respond accordingly.

Also, public schools are a state-run monopoly. And monopolies kinda suck.