I feel a big push behind this new policy is to remove the large amounts of commercially-broadcast TV content that is shoved into Google Drive and openly shared to 0.0.0.0/0 (e.g. via TV subreddits). Google has had fairly aggressive rate-limiting on viewing/downloading fully-open shared-to-all videos hosted within Drive for a long time, but there have generally always been ways around these limits. In the last few months, I have noticed several fairly large TV subreddits that used Drive for video distribution being closed due to too many DMCA takedowns, as such I feel that this policy change is G formalising their intentions to stanch this avenue of piracy, more than it may be a move to chase off malware/phishing ne'er-do-wells.

A lot of their takedowns come from user-flagging. If a user flags something, so that the item is now on the hosting site's radar, are they now responsible for it? They're only not responsible for things they are not aware of.