It's not all about profit as European SMS is now free. It is however about decentralisation stifling feature development - a trap we run into again and again, from email to IRC to SMS to Fediverse/ATProto.

WhatsApp is one company so if they want to enable sending images they can just do it, and they don't have to coordinate with anyone else. MMS was a failure because you couldn't be sure if your recipient would actually get it, or if your carrier would actually let you send it.