because it is privacy and encryption on the cheap
and you don't want to be busted because there is a complaint that the lawyers will now not file a complaint against one specific copy of the film but against all the people who uploaded a copy of the film (or thought they had) and so they will ask compensation or punishment against all the different uploaders as they know that that information is possible to extract
or this will be another thing that Kim Dotcom the big defender of freedomhosting hasn't thought about and has to change in the coming days or weeks
"The fact that encrypted data is not a total mystery to Mega is the most troubling issue. On one hand, the reason behind implementing a block-based data deduplication scheme is obvious: storage is cheap, but it's not that cheap, and the distributed infrastructure providers supplying storage to Mega don't have to waste space storing non-unique data—instead of 10,000 copies of The Hobbit, the service would only store a single copy, freeing up terabytes of space (though the scale and scope of the deduplication isn't known yet, so this may be optimistic). On the other hand, even if the service doesn't know those blocks of data happen to be The Hobbit, the service does know which users own those deduplicated blocks, and if one user is implicated, there's proof against all the others, too.
so do not include the name in the file
give the file another name or just a number and you take the note the real filename somewhere offline