One could have asked similar questions for the housing market:For one thing, it's hard to agree on what price [of higher education] should be the focus. Advertised topline tuition? Few people pay that. Average tuition paid? Average student loan debt? Is the bubble in higher education present at all universities, or just top universities, or just for-profit universities? And how is whatever rising price that is the focus connected to changes in the benefits of a higher education? Indeed, what are those benefits?
Average prices of houses paid? Average mortgage debt? Is the bubble in housing prices present in all neighborhoods, states, or regions (urban vs rural, safe vs dangerous neighborhoods). And how is whatever rising price that is the focus connected to changes in the quality of housing?
One has to take into consideration public education and government funding which is ultimately a price charge to taxpayers.
Looking at tuition only might be misleading. The price might stay constant but if the quality has gone down, there is also a bubble (prices are not going down to match a possible lower quality of higher education). Granted, I don't know of any comprehensive study on quality of higher education in the US [this might be an exception], but without one it is not possible to reject the possibility of bubble in higher education.