You are comparing public universities to private. Public universities have an obligation to accept a certain percentage of applicants from the state they are in because they are funded from taxpayers in that state. That could impact the statistics you are citing. I would imagine that the stats for OOS admissions at the public universities are comparable to the private universities overall stats.
Also, admissions is a numbers game. Those universities need to accept a higher percentage of students applying to get the number of enrolled students they need to fill their incoming class. As they get more applicants, that percentage will go down. However, because they have large freshmen classes to fill (of several thousand, versus a very small number at CalTech, e.g.), they will always accept more students.