He has to live with Outlook, which, like other mailing software, scans messages before they are sent for keywords such as "CV", "Resume", "Attachment", and, if it gets a hit, and there's no attachment, reminds the user "would you like to add an attachment?"
Unlike other mailing software, that dictionary includes "Bill". Every email he types his name into generates a "would you like to add an attachment", until he either disables the feature or sets up a signature.
Unlike other mailing software, using / will try to include a file, picking something that resembles the words typed, and by default attaching the file. On the Outlook 365 web client, not even Bill Gates can disable this feature. So, if Mr. Gates ends an email with the signature /Bill on then the helpful Web Client will find a sensitive piece of financial information and automatically attach it to the message.
Unlike other mailing software, Outlook gets bundled into office IT packages for companies around the world, supposedly to offer a comprehensive solution for your basic business infrastructure. Businesses end up including proprietary features and locking their users into Outlook. Sure, you can tell people to set up signature blocks, but you're as likely to get 100% compliance on that as with telling people they shouldn't use tab to indent their paragraphs.