Why in Schweser Book 4 page 13 Top of the page

Why in Schweser Book 4 page 13 Top of the page :”Start up and middle market private companies have more risk and lower returns than investments in established companies via buyout funds”? Shouldn’t it be more risk and higher returns?

I remember on the online seminar, the professor said the lower return means to be SHORT term lower return, but for the long time horizon, the return generally higher.