Well first off they're not "leaving," since especially nowadays the majority of Chinese students who finish their overseas education end up coming home. Another thing is that its one thing to build more educational institutions, its another thing to staff them. Simply put China is a frickin large country that only rose from poverty a little over a decade ago, so finding the talent and academic infrastructure to make sure those institutions are up to par is no small feat. Regrettably, no doubt in the rush to meet the demand for the amount of high school graduates every year, you get some institutions that are built up via corruption and thus low quality.
A prescient point too, but one that'll require a massive shift in the Chinese populace's way of thinking, is that simply put lots of people are not fit for college. College should be for people going in to highly specialized areas of work and many people simply waste their years studying something useless due to the expectation college is necessary for a high paying job. Meanwhile society has thousands of jobs that are essential and don't require a collge degree. In America at least, a lot of these like parcel delivery driver actually pay really well to boot. You won't know how many people are bamboozled they wasted all their years in college to make minimum wage, while their classmate who dropped out became a truck driver and already own a house.
With so many lost youth in China today, parents seeing the value in vocational work will definately require a shift in the way of thinking.
