While arguably it's Gmail's fault, there are email clients, such as Gmail, that do not behave well with, or perhaps support at all, emails as attachments. When emailing people who use Gmail (as personal email or as the host of their work email), sending emails as attachments just doesn't work well.
Well, yeah, sure, there is terrible software out there. But if you expect everyone you communicate with to live with terrible usability because you insist on using broken software, then you are just being an asshole. Email is an open, federated system, you can just switch to different client software.
