Remember that the creator of Mega is getting extradited to the USA - again - a country where he's never been, by the way - for basically this crime (using encryption).

Not true. He previously ran a site called MegaUpload which hosted copyright infringing files. This is why he created Mega, which is an end-to-end encrypted cloud storage service similar to OneDrive of Google Drive.

Even if Mega users host illegal or copyright infringing contents he can't be convicted for it. In fact, he won't even know about it.

I'm just amazed that not everyone is using it. People don't seem to know about it and they're not advertising it. They probably made a deal with LEA or politicians not to spread the word in exchange for not being extradited.