Mega isn't indexed and decrypts content in javascript on the client. If people are using it to share your stuff, you have to find where they're sharing it to even find out that it's on there. Now, Hollywood did this to themselves, because back when it was Megaupload the fact that they had a search index was used as an excuse to shut down the whole service because a couple of employees used it to access infringing stuff without taking it down, so Mega got rid of that as a means to prevent it from happening again.

Internet Archive is searchable and executes DMCA takedown notices. If something of yours is on there and you don't want it to be, it's not because they're making it hard to change that.