In terms of legality Megaupload messed up by directly participating in copyright infringement. They paid people to upload copyrighted movies. Cox doesn't reward people for copyright infringement. The lawsuit against them argued they failed to take enough precautions (for example cutting off subscribers upon receiving an accusation from a third party) and that should make them liable.

In practice Megaupload is not an established company. Other consumer file storage services such as Dropbox, Google Drive, Microsoft OneDrive, Apple iCloud are trillion dollar companies with deep legal benches and lobbying muscle. YouTube seeded the service with pirated content and Google helped fight off a copyright lawsuit by finding evidence that one rights holder uploaded their own video and then claimed infringement.