I believe it was mainly to detect when a user is trying to navigate to an intranet site with a single-word name (for example http://fileserver). To do that, Chrome needs to make a DNS request for the word and check if it's valid.
However, you can have misbehaving ISPs that replaces all NXDOMAIN responses with something (producing false positives for what constitutes "valid" hostnames), or a guest portal that is hijacking DNS responses, so Chrome will make requests for random DNS hostnames that are unlikely to exist to detect if DNS hijacking is occurring and disable the intranet detection if it is.
However, you can have misbehaving ISPs that replaces all NXDOMAIN responses with something (producing false positives for what constitutes "valid" hostnames), or a guest portal that is hijacking DNS responses, so Chrome will make requests for random DNS hostnames that are unlikely to exist to detect if DNS hijacking is occurring and disable the intranet detection if it is.