Why do users misunderstand the recycle bin as archive?

Today I faced yet another user misusing the application's recycle bin as archive. When I offered him to empty it he went angry because he "always did so" and didn't want to lose his mails. The first time this happened to me it was a Windows user with the Windows Recycle Bin, now it is a Thunderbird user with Thunderbirds Recycle Bin. Both users are long-time computer users, but without computer knowledge. Both have studied and are mature (the current one is a 60 years old man). This case happened to me quite rarely, but it makes me wonder anyway: Is this a more common problem? What makes people assume that recycle bins are archives? Is there something wrong with the approach to store files before deletion in a thing called "Recycle Bin"? Are there better solutions to delete objects, but have a chance to restore them?