It's a multi-faceted issue. The receiver has to have the ability to send read receipts and to have that feature enabled (some people don't want you to know they read your text), and the carrier also has to support that feature. If any of those conditions are not met, then you will not get read receipts.
Do you know if carriers determine if RCS chats in Samsung messages show up as blue instead of the green bubbles? I can see the delivered/read receipts so I know that aspect is working.
