The reason was the inadequacy of educational content for people with disabilities.

Employees of the University of California at Berkeley (University of California, Berkeley, UCB) began removing audio and video recordings of their lectures from YouTube and the iTunes U educational service on March 15 local time. In total, more than 20 thousand materials will disappear from the network within six months, reports the specialized publication Inside Higher Ed.
According to IHE, the reason for removing the lectures was their inconsistency with the Americans with Disabilities Act of 1990, according to which educational materials with an audio track must be accompanied by subtitles for people with hearing impairments.
According to an investigation by the federal Department of Justice in August 2016, captioning on much of the University of California's content was either substandard or missing.
After this, officials left the university a choice: to remove the materials entirely or to ensure that people with hearing impairments have the opportunity to use them on an equal basis with others. University officials said they could not afford costly content upgrades, which would force them to remove existing lecture materials.
UCB added that it will continue to publish materials online. For this, the university plans to use the non-profit eDx platform, which, although free, is available only to registered users.