That's a specific case where their client base literally does not care about the cost. $30,000 or $40,000 makes no difference to them.
Or, to take it further, it's quite likely a Veblen good: because only families that can shrug at $30,000 a year for private school will be going there, your kid will only associate with other rich kids, creating valuable romantic and professional networks.
That's a nice, oversimplified, right-wing talking point, but there also happens to be a huge disparity in per-pupil spending in Washington-area schools:
Also, The Education Law Center has found that low-income public schools overall spend $3,000 less per student than their wealthier counterparts, amounting to $75,000 less per 25-student classroom, yet low-income districts contain many more students likely to have higher needs due to poverty, English Language Learner status, or disability.
In other words, I'm sure the right-wing can cherry-pick anomalies (like they do with climate change, etc. and look like fools throwing snowballs on the Senate floor [3]) while disingenuously attempting to prop anomalies as "the norm", but the greater reality is that low-income areas tend to get less funding for students overall -- and, it's a problem.
Or, to take it further, it's quite likely a Veblen good: because only families that can shrug at $30,000 a year for private school will be going there, your kid will only associate with other rich kids, creating valuable romantic and professional networks.