At least in the US, copyright is a monopoly on certain rights for a limited time. By locking those rights for an extended time, it is stretching that definition. The time to benefit from your creations is in that time window. That goes for my creations, yours, and everyone else too. Public domain is patient, but I don't think it is worth depriving it of moderately older works with which others can start to use as a foundation to build upon.