Every piece is desired in some fashion. We want Outlook to open our attachments without having to explicitly choosing the program. We want Word to have those

Every piece is desired in some fashion. We want Outlook to open our attachments without having to explicitly choosing the program. We want Word to have those advanced macro features. We want Word to have hyperlinks to things on the internet. We want to be able to install things downloaded from the internet. In isolation, each of those things are desirable to some segment of the userbase. It just so happens that the chain basically allows you to install a program from an email attachment.